How to build a loft floor (STRONG)

A structural engineer shows you how to board out a loft the STRONG way. Get your floor joist design spreadsheet here: geni.us/floorcalculator
Did you know that simply boarding over your existing loft ceiling joists will not make a strong loft floor? Instead, you will need to create a floor by using new floor joists supported on loadbearing walls. In this video you will discover how to build a loft floor that is strong enough to carry the weight of people, furniture, storage, and pretty much anything else!
👷‍♂️Get help with your loft conversion geni.us/loftsurvey

[@RobindeJongh]

🍾I'm delighted to announce my new book, $0.99 for the next 3 days of the book launch geni.us/building

[@pefu512]

I'm from Germany. My wife and I own a former farm house which was originally build in 1923. The structure of the timbers carrying the roof is somewhat similar to what you displayed in this video. However the dimensions are quite different and certainly the standards applied to constructing such structures have changed a lot during the past century. I believe in the UK there are also a lot of historical buildings. I would be interested to see a video about how the craftmanship has changed in the UK during the past 100 years and how historical buildings compare to more modern structures in this regard. Your videos are very well illustrated and your clear speaking makes it easy to follow for foreigners like me not speaking english as their native idiom.

[@JC-gx8zs]

Thankyou for the spreadsheet, very helpful and just what we needed.

[@talatsharif9449]

Your videos are amazing, in-depth clear and concise . thank you

[@RobindeJongh]

✅Get the spreadsheet shown in the video here: geni.us/floorcalculator

[@dylanefford7869]

Hat off to you Sir.

[@bernardwarr4187]

Many thanks Robin. As a property maintenance and repair professional, I can confirm, we are regularly are called to checks on floors, and carry out repairs to the junction of the floor sheeting, where it’s previously unsupported

[@bernardkehoe7610]

Yes robin this is brilliant I am going to download this spread sheet calculator this is exactly what I need. keep these videos coming. Legend.

[@leonopensstuff]

Excellent video, it's been a while since I've learned so much in such a short amount of time. Thank you!

[@_christianlowe]

Great video! Really appreciate you creating this. Thanks!

[@mikejames4540]

I really appreciated this. I live in a house built in 1907 which, by and large, is over-engineered. Part of the eaves have been converted into storage by being floor-boarded and I was horrified to find that the joists supporting the ceiling below the storage area are 3 inches by 1 1/2 inches. (Approx 75mm x 40mm). Naturally, there is some cracking on the lath and plaster ceiling. Having used your calculator, I now know exactly the dimensions I need to create a safe storage area which will not damage the ceiling. Thank you so much, Robin!

[@ThePinkPanth3r]

The ceiling joist in our 1900 home are oak and nearly 3inches x 8, not enough space to really use for storage though. I only really use the access to run new electrical.

[@Mole-Skin]

I am a retired Carpenter/joiner and have worked in the residential sector all my working life.. In the very early days I was working on a loft conversion with a couple of guys.. they cleaned out all the rubbish between the existing 4" x 2" Joists in the loft and screw fixed additional 4" x 2" timbers on top at 90 degrees to create a lattice.. Every joist was screwed down to the one it passed over and it created an incredibly rigid floor.. I did not realise until a lot later that 'You cant do that..' became the response if I dared suggest this option.. Considering how succesful this option was it has always bothered me why literally no-one has looked into this as a construction method. The load spreading is incredible and I would love to hear an Engineers opinion..

[@mste456]

this sounds exactly like what im plannin in my loft, just a small 9x10ft storage area for light things and a network cabinet

[@Mole-Skin]

@@Sionnach1601 Not if the ends of the new joists are supported.. (Actually it works even if you dont..) I am no structrual engineer but I witnessed the procedure and it is the spreading of the load by connecting the existing joists to the new that gives the rigidity.. A 'Latice' is the only technical term I can think of.. By way of example.. put two scaffold boards side by side across say an 8' spacing and stand in the middle with one foot on each board.. it is quite bouncy.. now clamp the boards together in the middle and it becomes far more stable..

[@mikeyf4744]

I think it can cause cracking of the ceiling underneath so now needs to be separate

[@peterpage7322]

That idea sounds very feasible, quite often a structural engineer will suggest doubling up joists and screwing them together.

[@Nerd.Immunity.]

This might be the most technical loft floor video ever made!

[@dpiddy82]

Just about to undertake adding some flooring into my loft eaves for box storage - I have a general idea but this has focused me a little more! I’ve watched a few YT vids but this is definitely the most useful. As a CAD engineer myself the CAD visuals were very helpful!

[@RobindeJongh]

Glad it was helpful!

[@Flash1857]

Thanks for the advice and videos

[@DaveRaval]

Thanks for the detailed video! Can't fault your structural work :) However I do have some questions about the insulation, please. Modern building regs require a U-Value of 0.16 in England and Wales and Northern Ireland (for retrofit, it's higher for new build and in Scotland), so if the floor of the loft is insulated, then you need to leave space for that. The most common mineral wool (k value of 0.044) would require a depth of 270mm, plus the BBA recommends an air-gap of 50mm above that to allow air to flow from eave-to-eave, to prevent condensation forming on the bottom of the boards. So, just as a suggestion, perhaps either your calculator tool should have a minimum height of 220mm, or if someone wants less than that, there could be a warning flag up to say that a higher grade of insulation is required or that under-rafter insulation should be used instead, to make it a warm loft with the eaves sealed? What do you think? Cheers :)

[@elvispresley7844]

Fabulously well explained Robin. Calculator fabulous too 👍

[@steady803]

Thanks mate. Very useful 👌

[@Honey4myHoney-fv2wu]

Brilliant video mate

[@Ja5onB0urn3]

Hi Robin, great video explaining how to do it differently. Your CAD example is near identical to my loft, apart from a chimney breast on the party wall. We had a new roof on our 1950s house last week and I took the opportunity to ask the roofers to lift in twelve 6x2 joists up into my loft when they stripped the old roof, ready for me to crack on with in the coming weeks. Watch this space. (Liked and subbed) 👌

[@patriot77185]

Great video very informative thank you.

[@stevep1050]

Hi Robin, thanks for the videos. It would be great to see how you'd deal with some of these loft conversion concepts on a building with a hipped gable, like a 1930s semi. I'm wondering how to deal with the height constraint between the wall plate and the pitch of the roof when using timber beams or joists.

[@Newmusicreview]

Dude...this is exactly what I'm looking for ...thanks ;-)

[@Benbearjones]

I really appreciate your videos we are a young family on one wage trying to modernise a 50's semi and the info that you give out is invaluable to me I don't have people to ask. I'd love to ask how are you getting the large joists in do they have to go through the roof moving tiles I'm guessing because they can't be cut. Thank you

[@thomo74]

Great video. Very informative. There is tongue and groove structural chipboard flooring available which locks together. It’s really good for applications like this 👍

[@gregwalters4656]

Hi Robin. Really enjoy your video's and have learnt a lot watching them. As far as I'm aware you as long as you glue the joints on t&g flooring it doesn't need to sit on a joist. Also you could set the joists at 400mm centres to make the 1200mm total

[@RobindeJongh]

Great tip! Thanks Greg.

[@cha1ny104]

This is amazing, thank you so much. How important are the ceiling binders? My Victorian property has this exact arrangement but without the binders

[@stevenewbank]

I would be interested in your views of loft legs and similar products.

[@StagvanHeuten]

Good video

[@mohdchaudhry]

Hi Robin great work! Is there a calculator which takes into account the what the span can be in the loft if you double or triple up joists and bolt together?

[@nickybackshell790]

Hi grate video would love to see how u would do the floor with out a supporting wall in the middle but a 12 by 3 beam from frunt to dack

[@osmag2194]

Thanks Robin. Great video and easy to understand. I am curious to ask if there should be a gap for ventilation between new insulation and new boards? Many thanks.

[@kenantaylan3617]

Any plan for basement videos or wind calculations.

[@Sleekitnuts]

As a joiner I would space the joists at 400mm centres, less cutting, less waste.

[@ianhand66]

Never knew this. Ive partly boarded each house ive owned , straight onto ceiling joists just for storage . Not on my next house eh. What was a quick diy weekend job is now maybe quadrupled in price and time but the right way to go about it.

[@RobindeJongh]

Hi Ian. Bear in mind this video isn't the only way. It depends on your tyoe of roof and where your loadbearing walls are.

[@richardwood4541]

Hi Robin great explanation and thanks for the download of the span table. I have a quick question please if I may. Can I retro fit a build in joist hanger by cutting a slot into the brickwork and tapping it in? I’m struggling to get 100mm face fix Joist hangers without paying a silly amount of shipping. Thanks for the help 👍🏻

[@jimslama990]

Hi Robin, excellent presentation! What software are you using?

[@SafarWIP]

6:15 do you have video about how to do flooring for this kind of loft? The Truss one, I have exactly like in this video from that time stamp

[@philflip1963]

Having an overhang on a board beyond the edge of a loft floor joist is not necessarily a critical point of weakness IF the loft area is intended for low loads/usage, (only storage and occasional access) AND if, (as you have indicated) the boards are bonded/staggered IF relatively narrow, (eg. 300mm) tounge and groove boards are used since the overhanging board will be supported by the tongue and grooves of the adjacent staggered boards.

[@MarcusT86]

Great video buddy and thanks for the calculator. So if I want to create some storage for static loads like Christmas decorations, and other bits, should I still hang some joists off the shared party wall to external wall of my semi-detached house?

[@RobindeJongh]

I would suggest reading up about party walls first, as I can't legally advise on this.

[@jamesjackson2998]

Great video……im thinking of doing this…..however, how would you fix those hangers to thermolite brick? It crumbles so easily.

[@dj0men666]

Great video thank you. Got the calculator but widths etc are fixed. Most of timber places sell for example are 45 or 47mm width but the sheet has 50mm. Is it ok using the 50 for those instances as you cant put exact. Also if i fitted a wall plate to stone wall at one side am i best adding joist hangers to face or just sit the joist on the top of the plate? The wall plate would be fastened with decent sized frame screws at multiple points along it. Thank you. 👍

[@walterarmstrong3117]

Hi Robin, very informative series of videos. For light storage is it possible to use the ceiling binders to support 3m 2x6 timbers, as the binders are themselves supported on internal wall & party wall?

[@RobindeJongh]

Hi Walter. The ceiling binders are most likely not strong enough.

[@Speedy6240]

Can the joists sit in brackets/hangers on both sides of the wall or do they have to be supported by a wall on 1 side?

[@paul2001anderson]

do you have any calculator for calculating I beam steel gable to gable ? thanks. not a builder just trying to price up materials for my house

[@wellwisher2673]

You mentioned a few times that it will good fo storage but would this conversion be suited if you were converting it to an additional bedroom?

[@handymistry3156]

Excellent videos and really informative. Do you offer any service for loft conversion design? It would be great to see examples of lofts that can’t be converted and not just because of height restrictions.

[@ashihtaka]

Robin what is the software you are using in this video?

[@bernardwarr4187]

If the end wall is constructed with a Thurmolite type block work, what’s best joist hangers or fix a timber joist to the wall? What is the required of a fixing medium?

[@funninja1405]

Hi I have question - I have loft with 3 angled roof and 2 floor binders are very close to the middle and spaced about 1 m away from each other and sealing joists are nailed to the roof joists and not on the outer walls bricks. It looks like the wall are about 0.5m away from the point where floor joists are joined to the roof joists. Thank You

[@user-yn4ld8me9w]

in normal loft space, if you put those beams in you will have a head height issue. they will only work in high roof space loft

[@Franz10mp]

Hi Robin, all very helpful. Thank you. I am however thinking about the practicalities of foing this sort of job when dealing with an existing loft. The only way to take long timbers in a loft is through a loft hatch. This makes the task impossible if we want to keep those long timbers all in one piece because there won't just be enough space. So, would it be possible to cut timbers, say, in halves and then put them together somehow once in the loft? How could the timbers be put together again in a structurally safe way?

[@RobindeJongh]

Hi Francesco. There is no way to splice a timber to keep it structurally sound. For longer timber joists you would need to remove some tiles and take them through the roof.

[@mytelly-4222]

Could you tell me where to cut the joist for the hatch ?

[@rickyjay4792]

Robin , firstly thank you for the videos very useful and educational , Q: instead of using joist hangers , providing enough fixings where used could you use joists along the wall to support the floor joists ? thx again Rick

[@RobindeJongh]

Hi Ricky. If you got the fixings and wall-plate designed by a structural engineer, you should be able to do it this way, yes.

[@dalroth10]

Hi Robin I am looking to create a storage area in the roof space of a small (3.6m x 3.2m) ground floor bedroom extension at my daughters house. The exterior walls are 275mm cavity, 102 brick 75 cavity, 100 block. The roof is a cut rafter design and spans the 3.2m dimension. The roof pitch is 42 degrees and the length of the roof is 3.6m. There are two 150mm x 75mm wall bearing timber purlins, (at mid span of the rafters), and one 150mm x 75mm wall bearing timber beam at mid span of the ceiling joists. I would like to span the new storage floor joists in line with the rafters, sitting on top of the wall bearing ceiling beam and being supported at the ends via short hangers fixed to the wall bearing purlins. In effect creating a small "cradle" spanning 2m. I've downloaded your floor calculator (thank you very much for this) but don't think I can use it for the arrangement I've described. I realise the ceiling joist support beam and the two purlins will carry some load, but the storage area will only be a 2m wide strip along the 3.6m length of the roof, minus the loft hatch area. It will also only be about 1.1m high at the ridge and used for storage of very light items such as empty suitcases and Christmas decorations. Any help or advice on this small domestic project would be very much appreciated. Kind regards, Robert

[@pratikdesai8355]

Great video. What are the structural implications of using OSB or structural ply to board out the loft? If the boarding has structural value then does that further limit the need for deep joists? Or is the idea to have the joists pass requirements and the boards are just a structural bonus? Hopefully that makes sense and is not too silly a question.

[@RobindeJongh]

Hi Pratik. You're exactly right. The joists are the structural element, and the boards are a bonus if they stiffen the floor up.

[@millin2222]

Can I ask what loft floor joist would you use for 270mm, 300mm clearance for insulation and

[@inityo]

After you nailing the new joists into the wall? Or they can just hang on top of the old joist??

[@mohinderkaur2955]

Do you fill the bottom with insulation or not before you put boards in there ??

[@francoisnel7769]

Im Semi detached and have only 1 wall to attach hangers too. Is there a main beam on the other side that can support the weight?

[@crazyethanyeahyeah]

Hi Robin, Great informative video. What CAD / design software are you using? I am also curious if you use Formply plywood for the flooring? Many thanks, Ethan - Australia

[@statuescher]

It looks like he’s using Sketchup for the visualisations.

[@uittyman]

At 7:11... the way the run the 2x8s and double them ...if you put two 2x4s stacked on top of each other to get a 2x8 then doubled that stack and put them side by side then stapped them with metal plates to keep them together... would it have the same strength and be able to handle the spans?

[@frankdoyle3493]

Great video, can you run the joists to load onto the floor binders also?

[@RobindeJongh]

Not without strengthening them first.

[@abakhi]

I have seen on other videos suggesting to install Loft Leg directly on the joists and then floor boards on top of them. My question is why can't we install floor boards directly without addional joists? its on new build houses?

[@scottbramley1778]

My 1960's semidetached bungalow loft is 10m from gable wall to gable wall, would the principles in this video still apply? Could I use 2x 5m joists meeting in the middle to span the new floor? Could you please cover something like this in a new video as I don't see much on bunglaows. Thanks

[@robertszynal4745]

I have this similar issue except mine is 17m between the gables!! I expect we'd have to find a way to transfer the load down to the ground at points along the way, such as through internal walls or by adding pillars.

[@scottbramley1778]

@@robertszynal4745 I had a quote from ecotrus for just a conversion, no dormers, for £47+vat. I think RSJ's would be cheaper

[@Gubbsey]

what CAD progrmme are you using?

[@ellensicat1825]

I’m from the Philippines. What is the best material for loft flooring? Our contractor is planning to use 3/4 inch plastic panel instead of marine plywood. Will it last and is it safe?

[@pompeyjim]

Nice spreadsheet but it's not letting me use 45mm thickness timber?

[@ZafarKhan-ip1um]

Can you please do a video on ridge beam size calculation.

[@RobindeJongh]

Hi. It's here: kzbin.info/www/bejne/eaqopIt8frN6jK8

[@jasbansal2079]

Great videos… may I ask what software you are using for the illustrations?. Thanks Jas

[@Frazer20]

He’s using SketchUp (pro)

[@MrChris9486]

This is brilliant thank you. The calc is good also. I can't find 50 x 175 timber, it's all either 45 x 175 or 47 x 175. Will this make a huge difference?

[@RobindeJongh]

Hi Chris. 47mm is fine to use for 50mm.

[@johncoppock3823]

Huge thanks for all the great videos. Silly question: If you do the work yourself as an amateur project what is the best way of finding a good BCO please?

[@RobindeJongh]

Hi John. The local council BCO might be a good first port of call.

[@johncoppock3823]

@@RobindeJongh Funny I used to assume/think/guess that but now I'm not sure as I'm guessing council planning departments may be overwhelmed with work from all the new build estates (?) I guess it all depends on the area, and local factors.

[@livingladolcevita7318]

Great. I am considering loft conversion but the walls upstairs are studded and I have not long had the roof re-slated so probably a no go if I need to install flitch or steel beams.

[@bernardwarr4187]

What’s your thoughts on insulation below the new loft floor? I think we’re looking for average 280mm, a cross the surface, using 300 between the joists

[@RobindeJongh]

Hi Bernard. People tend to do something like 100 rockwool between existing rafters, then 170 between new joists.

[@umbertogiannini]

great video, this is exactly what i want to do in my victorian loft however, i do have 1 question. Instead of attaching individual joist hangers into the brickwork you mentioned a wall plate! how would i attach a wall plate and secure it to really soft victorian brickwork? just screwing a piece of wood to these bricks would really worry me.

[@alex1975uk]

Great question, but before that ask yourself how are you supposed to get 5 or 6m long joists up there!? Raising the new joists up is whack if you ask me.

[@APSuk2]

Hi Robin, looking to board out my loft and am using your calculator for the joists. My span from wall to wall is 3500mm with 500mm joist centres, if I use a 50mm thick by 175mm deep C16 grade joist the calculator says this will pass but I am not able to source this size of timber locally. I can source 47mm thick by 200mm wide C16 joists but the calculator does not allow me to input 47mm for the thickness. Do you think this size of joist will be suitable? Thanks Adam

[@RobindeJongh]

Hi Adam. The 50x175 is a rough size.

[@chrisanderson8578]

Discovered your videos recently and they are great but I'm always left wishing you'd cover a standard 1930s semi because the videos never quite fit my use case. Great work though.

[@adammawdsley7778]

Hi Robin could you do a video on how you would do this kind of work on a hipped roof with perlins

[@RobindeJongh]

Hi Adam. Yes I hope to soon.

[@Ihaveguitars]

Why not use tongue and groove OSB? Readily available in France.

[@muddin8097]

Hi Robin Thanks for all the videos. My question is in relation to a typical London Victorian mid-terrace house (4.5m wide). If the whole building is empty and the ceilings are all being knocked out anyway, and you have the option of removing and adjusting all the ceiling joists, what options are there for a more efficient use of space and materials. For example, can new floor joists for the loft be placed on top of the existing front and back wall plates and in the middle placed on the spline wall, thus avoiding the need for steel beams for the loft floor? Separate to that, is it possible and worth lowering the hight a first floor rooms (from 2.6 currently to 2.4) to add a bit more room in the loft? Most loft conversions seem to be designed to, for example, not disturb the ceilings below, etc., but if none of those were an obstacle, rather the only limits were the outer shell of the building and, of course, building regulations, what could be done? I have some other thoughts/ideas I can add if you think the general question has value. Thanks

[@RobindeJongh]

Hi. Happy to answer your question: geni.us/askrobin

[@GaryW10761]

What about a timber frame house?

[@user-fs8pf2rt9z]

What is the computer program you are using for this please? Great video

[@Frazer20]

SketchUp

[@Aliens4world]

Very good explanation and most of things coverd but most basic questions remains unanswered which is floor joists which will be probably 3 or 4 meters long will go in loft throuh tiny loft access??

[@RobindeJongh]

It's not easy. Would have to lift tiles and go through the roof or create a hole in the gable wall.

[@Jj-ff9vq]

Really good lesson...my roof runs long and i dont really have a wall to run the new beams to once off the gable end, the next wall is the other gable end about 30 metres away. Its a trussed roof design. What to do?

[@RobindeJongh]

Hi. No problem - see my video on what to do when you have trussed rafters here: kzbin.info/www/bejne/r4qvdmqvj9Z0q7c

[@Jj-ff9vq]

@@RobindeJongh cheers Robin i looked at that but it is within a context of a loft conversion, whereas i only want to put some storage shelving into the trusses, with a central zone to walk on to access the storage. Its that central zone that i want to put independent support beams in for, but as it is exactly like this separate video youve done theres no obvious walls to join those beams to 😔

[@solomonsmith3658]

Hi Robin, my loft has been converted by previous owners but they have just placed boards directly onto the ceiling joists. I want to fix this however there isn’t enough headroom to add a structure above as you have shown. Can it be done in parallel to the current joists bust just slightly higher? I was planing on supporting them by the Perlins since there seems to be secondary perlins low down near the ground. Does this sound reasonable?

[@fujimotosan9123]

I would go with parallel as opposed to the video installing them perpendicular, because you would decrease the joist space. See it in the calculator. If you absolutely want to make sure the joists don't bend, use the same joist sizes and another layer of 18mm OSB floor boards perpendicular underneath. And keep the piano downstairs ;)

[@johnkennett3265]

Excellent details on practical solutions to real life situations to multiple variables no matter where you live. I am a retired Canadian living in a small Philippines fishing village where home construction is by home owners who build using rough chain saw lumber on soft wet ground. This video stressed thinking from the ground foundation upward leaving NO weak points anywhere.

[@RobindeJongh]

Thanks John. Glad it was helpful!

[@ChrisLivingInYork]

I made the scoreboard DIY error of doing exactly what you suggested, not doing in the video. My question is without removing the the roof tiles how would you get approval side lengths of timber through a standard size loft hatch.

[@RobindeJongh]

Hi Chris. It's not always possible to do the construction without removing tiles, or even some bricks in the gable.

[@davidtaylor332]

Good informational video. Shame you cannot download the spreadsheet without signing up for some expensive download sites

[@RobindeJongh]

Hi David. Thanks for the feedback. I'll look into that. Do you mean that my website requires a log on?

[@jpreesecolligan]

Change the joist centres to 400mm and the floorboard would work out without having to cut. The floorboards come in at 1200mm and work out perfectly with 400mm joist centres.

[@sulimgalaxy2078]

Hi Robin, would it be ok if you instead have the joists on brackets from end to end to avoid having to pocket out a load bearing wall.

[@RobindeJongh]

Hi Sulim. You would need to get some joist hangers that are designed to fit to the face of the wall. I believe Simpson Strongtie do some of these - www.strongtie.co.uk/en-UK

[@sulimgalaxy2078]

@@RobindeJongh sound thanks.

[@Speedy6240]

Aren't the hangers timber to timber hangers you're using in the video

[@JohnnyWaveslayer]

What program is this?

[@davidgibson8523]

what CAD software please?

[@ivan1u2be]

why not just put 2in rigid insulation on top of joist then 3/4 plywood?

[@yousufb93]

What software is that

[@olivermarsters816]

I have a truss loft set up and I'm trying to board it out and raise the height because of the thick insulation but don't want to use crappy plastic stilts. Can I use this concept to fit floating joists on hangers then board?

[@RobindeJongh]

Hi Oliver. As long as the new joists are supported at the ends by loadbearing walls, or a structural beam.

[@olivermarsters816]

Cheers buddy 🍺 thanks for replying

[@mrt2799]

When insulating can you use 100mm insulation inbetween 120mm joists?

[@prodical666]

If your insulation is not packed in tight with no airgaps between joists, its almost useless.

[@soarlikebird]

I’d be interested to know a work around in a 50s detached bungalow (so no gable wall to fix hangers/joists). Could you span wall plate to wall plate parallel to existing ceiling joists, but keep separate from the ceiling joists, and pack slightly under the new joists to separate from the ceiling below?

[@soarlikebird]

Purely for light storage

[@coolmonkey619]

I cant get such long wood up their what i do

[@Accomplice23]

How would you approach this if you don’t have an internal load bearing wall?

[@RobindeJongh]

See my other loft conversion videos on this 👍

[@michaelgraham7301]

Out of curiosity. I want to do the same in my bungalow, however, the distance from end to end is approx 10m. What would be the solution using your method as i will never get 10m lengths through the loft hatch 😂 Thanks in advance

[@RobindeJongh]

HI Michael. If you need some solutions for this, take a look here: geni.us/loftsurvey