Through Ventilation Cross Ventilation Explained

[@karlbadham8775]

Thanks for all these very informative videos. Steve kindly helped set my mind at rest by answering a few technical questions that arose from awareness of potential problems based on researching this excellent information sharing. Outstanding work Steve.

[@SteveRoofer]

Glad to help!

[@proactiveflatroofing7655]

I have to say Steve, I have been watching your videos for years and love your enthusiasm and practical fact based explanation of the "right" way to put a flat roof together, I would love to have a coffee with your sometime.

[@steveturnbull9869]

great information, I don't even work in the building trade but I find these videos fascinating and it almost makes me wish I was a roofer :) Steve helped me with an issue with a cold roof a builder did for me where it was condensing badly and I had to tell the builder myself what needed to be done after I'd watched some of these videos. Fast forward almost a year and my cold roof is now completely condensation free. Originally I had no ventilation at all, then I only had ventilation at the front, which still didn't fix the issue. Now I have through ventilation just using round soffit vents at each end section and its made a massive difference. All the timber is now dry on the deck above the insulation where previously it was sweating and mould forming. Keep up the great work with these fantastic videos.

[@SteveRoofer]

Thanks for the comment

[@jamesdiver2183]

how did you know or find out it was condensing?

[@steveturnbull9869]

@@jamesdiver2183 because water started dripping out of the plastic facia overhanging roof at the front of the building and it was brown and smelled like wood. I also pulled down a couple of downlights and used a torch and could see water droplets on the cables and moisture on the deck above the lights. It’s been still perfect since. With no vents it’s like a jam jar of warm water with the lid tightly sealed

[@benchippy8039]

No wonder so many get this detail wrong, there’s not much information about. Thanks Steve, never really contemplated just how ineffective ventilation is without through flow

[@SteveRoofer]

I was amazed also

[@benchippy8039]

@@SteveRoofer every building inspector should watch this and advise builders accordingly

[@wotnoturbo]

Thanks for taking the time & trouble to explain. 👍🏽

[@SteveRoofer]

No problem 👍

[@MrAlexshellard]

Just totally changed how I planned on insulating my garage roof, thanks dude!

[@SteveRoofer]

Glad I could help!

[@HarryASMR]

Using smoke to demonstrate your point? You’re a mad lad 😜 but also dedicated! Thanks for yet another super clear, informative video Steve!

[@SteveRoofer]

Much appreciated

[@_Mark_H]

Best way to give a visual demonstration as to what’s happening, can’t see air 😊 Nicely done Steven 👍🏼

[@northeastcorals]

Great video, I had seen cross battening before (probably one of your vids) but pretty much forgotten about it. Glad you reminded me of it's benefits as I need to build a little flat at some point roof this year.

[@SteveRoofer]

Glad you enjoyed it!

[@justinstevenson2061]

Very good stuff. I always use a steel/aluminum head flashing from the sloped roof to the flat roof with perforations in the metal to ac lol posh two things. First is your using the head flashing to provide waterproofing to the sloped roof, also then having the perforations (facing downward on a crated lip to avoid leakage) to have airflow coming in.

[@justinstevenson2061]

But this is some good stuff. So many people don’t vent flat roofs properly. Also, now they use spray foam and say now you don’t have to vent….. stupid…… Yes spray foam works as insulation and vapour barrier. That is sweet. But fibreglass bats act as insulation, and poly or similar acts as vapour barrier. Still need to vent either way….. The spray foam is better R value per inch but still loses heat, and you’d rather that lost heat escape rather than form condensation. A properly insulated and vented roof lasts so much longer.

[@trzmielol]

Your lessons are pricless!

[@nofurtherwest3474]

Yes, KZbin is great for many things

[@joefanningartist]

What happens when you screw the drywall it's going to make a whole in the vapour barrier?

[@davideyres955]

Watch his other videos on vapour control layers. He talks about the use of butyl tapes which effectively seal the hole. The point is to make sure you make it as air tight as possible.

[@wac7567]

Hi. Have you done a video where the cross ventilation on the flat roof (garage conversion) is running into a pitched roof of the house. Or a video where there is no space for soffit due to boundary line - vents would have to go under in the facia boards... beneath the gutter level, if at all possible.

[@angelkj]

Thanks for your videos, your real world examples are very interesting. From what I know, air moves only due to three reasons: stack effect (i.e height difference), wind, mechanical (fan). On flat roofs we don’t have any stack effect, we don’t install fans, and wind is unpredictable and maybe inexistent in some circumstances, so almost no air will flow through. The experiment is explaining the theory nicely but I think it’s not indicative of reality. I’ve seen in some countries building regs venting being only suggested above a certain pitch. Curious to hear your opinion on this. Cheers

[@SteveRoofer]

My opinion is don't do cold roofs, do warm roofs then you don't have to vent

[@angelkj]

I agree… a warm roof is the way to go for flat roofs. That would be a better suggestion as venting a cold flat roof which has no airflow makes no sense. Moisture will just stay there. Especially on balconies with parapet walls where you have zero airflow…

[@SteveRoofer]

Balconies are alway a problem no height for a warm roof because of the door step

[@steveturnbull9869]

@@angelkj I've found even on a calm day when you think there is no wind at all, there is usually a small amount and it's enough to create a through draft.

[@paullovesey4863]

Genuine question. If you can’t put a hole in the vapour barrier, how would you fix it?

[@SteveRoofer]

You just repairing with type as long as it's airtight it's tight.

[@adamkingdon8063]

Skylight on a roof with all the insulation installed properly with adequate vapour barriers and a vent on all four sides does this pose a security risk?

[@SteveRoofer]

Yes security is a problem however most skylights come with bolts that are temper proof

[@shawnodonnell441]

I have a residential roof with four pitched shingled side and a flat roof. The unfinished attic uses a few shingle vents. We are looking to finish the attic yet we do not know how to vent the roof or apply insulation.

[@SteveRoofer]

If you'd like to send me some pictures I'll certainly have a look and give you an idea

[@Elites-asthetic]

Great video So how does this work but on a pitched roof ? Insulation. Vented soffit and so on

[@SteveRoofer]

I will do a video on that in a week or so

[@andrewthomson8211]

Hi Steve, I have cut through my membrane and installation to fit spotlights. Now I have sweating on the underside of my roof. As an option, I thought I could install surface mounted ceiling lights and fill the downlight voids in with installation, Sliver tape, and plaster board. Do you think this would solve the sweating issues? Kind Regards, Andrew

[@BilbosBrother]

How does the cross battening work with furrings on a flat roof with a sky light?

[@andreicotorobai731]

thanks for video , how to do if joists are fixed on wall hangers inside the building? is a cold roof , bcz of building hight ..thanks

[@allysoncipollone890]

I have a room that i think was a patio that the previous owner closed in. I dont think there is any ventilation and im not sure what to do 😅

[@mrmikepark]

Could you drill vent holes in joists to allow cross vent between dead spaces around sky light if it’s a new skylight in an existing cold roof without battens.

[@SteveRoofer]

You can do but it's pretty much frowned upon I've shown people doing it in some of the videos but I would never do it vent the vent the roof properly

[@mrmikepark]

@@SteveRoofer only other way would in theory be to mushroom vent through the roof in each compartment on either side of the roof light. Ideally he would of done the battens to allow cross vent but roof finished now on top. Looking at doing multiple c.100mm vents through walls either side of extension into the space above insulation. Was gonna drill through joists to allow cross vent around roof. I don’t particularly want 10 vents up there penetrating the roof. 🥴

[@pauldavies7251]

Hi Steve What's the best way to ventilate a lean to flat roof which has got a glass lanter in the middle

[@SteveRoofer]

As explained int he video cross batten the roof

[@pauldavies7251]

@@SteveRoofer what would you suggest if there's not enough height to double batten the roof! There's a balcony patio door cill accessing the flat roof which is only 80mm above joist level!! Really appreciate the reply thanks

[@SteveRoofer]

Something has to give! how about putting ventiationa round the skylight? ugly and hard to do

[@pauldavies7251]

@@SteveRoofer really appreciate the reply Keep up with the great information

[@miker9980]

What are those two white (fascia) panels called? The one you're holding at 1:10 with the small lip and the one with holes for ventilation. I just can't seem to find these panels available anywhere.

[@multirole240]

I think you are referring to the plastic sofit and fascia panels. These are often overlayed on to the existing wood soft and fascia.

[@SteveRoofer]

Yes thats corect

[@jeromeclatot1769]

I wish I could send you some pictures I have 11 skylights. I’m not sure there is vents in there.

[@baloo217]

Hi, i love your videos, but, i don't see any that applies to my case, can you help me out please. I want to put an a/c on my garage, now, i live in florida usa, summer are very hot here, my garage has a flat roof , the walls on both sides are made out of blocks and stucco, my rafters go from block wall to block wall, and on top of the rafters is the playwood roof, so no air movement it all ..how can i insulate my roof? I will hate to have moisture on the playwood. Can you please help me? I will appreciate it. Tks

[@SteveRoofer]

If you'd like to send me more information by email [e-mail] perhaps I can help you

[@DaveSiggins92]

Could you leave 25mm gap instead of a 50mm gap and use cross battening with 25mm batten to make up the 50mm air gap needed?

[@SteveRoofer]

Yes I think that's the way to go. 50 mil is better than 25 mil, but when you've got cross battening you've got all sorts of flow of air

[@coreydwood]

if I cant get that thick insulation board u have above plaster,, can i use styrofoam.. for my 10 by 14 ft extention

[@muso31]

Any thoughts on plasterboard for the ceiling? I was planning on using 12.5mm tapered edge but is insulated plasterboard useful in a ceiling (flat warm roof) ?

[@JohnSSSSS]

What if you have no roof vents at all (old house)?

[@SteveRoofer]

Lots of old houses didn't have vents and they vented naturally because we double glaze get rid of our chimneys and so on. We now need to add ventilation so keep assessing your property to see whether you think you should add more ventilation.

[@CarlBurnss]

i build a flat warm roof, but i want to close it off with plasterboard, do i have to ventilate the space between the beams ?(with inside air)

[@coldt1484]

Hi Carl, the answer is definitely no, you must very tightly insulate the perimeter of your warm roof from the wall head upto the underside of the sarking. It's critical to make sure the roof is sealed. The warm void between the rafters is just that, a warm void that you can run cables for recessed lights. If your flat roof buts against an exiting pitched roof, you again must make sure that this junction is tightly sealed and that may include a soffit. Additional low level ventilation may be required to the existing roof. A warm roof is far superior to a cold roof which should be avoided where possible.

[@CarlBurnss]

@@coldt1484 thanks, I'm happy with that

[@davidwinter2166]

Hi Steve, when cross battoning...is it best to put the battons on top of the joist or ontop of the firings? Thanks

[@dannymurphy1779]

I have no sound after 2:40 the start of the smoke test. Is it like this for everyone???

[@SteveRoofer]

I've tried it and no one else has complained try it again please and get back to me

[@Tom_Hadler]

Sound is only left channel at that moment

[@dannymurphy1779]

@@SteveRoofer Thanks - sound now working! KZbin is a mystery sometimes :).

[@ir7868]

Brilliant how can we make slop in flat warm roof ( for rain water ) ? Help

[@theetheeyog9878]

Hi pal what if I use spray forum insulation

[@coldt1484]

This is a real challenge, you need to concider the roof make up, foam usually needs to be sprayed to the underside of a breathable sub-strate and sheet sarking is not regarded as breathable. Check the BBA certification for guidance.

[@SteveRoofer]

I'm not really up with spray insulation because of two things it's hugely expensive and the gassing off i.e. the smell the fumes and the health problems reported I've just not worth going there

[@domenico1403]

Where would you put those ridgeline vents?

[@matteastwell1198]

Hi. Thanks for the videos. They are really helpful, so basically if you have a cold roof the only real option is a dropped roof. I’m looking to convert a summer house into an office, with no room to drop the roof? Am I buggered.

[@SteveRoofer]

I think buggered is a bit Strong but yes you are right why not do a warm roof

[@matteastwell1198]

@@SteveRoofer just height issues is what’s stopping me doing a warm roof.

[@AntonWardo]

Hi Steve very useful videos on your channel. What would you suggest for venting a flat roof which is enclosed by a building on one side? Thanks

[@SteveRoofer]

We would use abutment vents there's always a way of doing it it's just a matter of detailing in cost

[@AntonWardo]

@@SteveRoofer thank you for your reply. I came across your video on abutment vents and it was most helpful. Thanks anthony

[@SteveRoofer]

@@AntonWardo not a problem

[@AiwaLee]

How about mice or other vermin getting into those holes?

[@dalturbo]

Thank you so much 👍🏽👍🏽

[@coreydwood]

if I cant get plaster boards,, can I use chiprock walls

[@SteveRoofer]

I don't quite understand, can you elaborate?

[@MrTwinkieeater]

I mean it seems elementary. If you want to go through the wall, put a door in it. Same thing.

[@markbridle3349]

Backward and forward backward and forward 😃

[@philsims6607]

High Steve, I was watching this video from Robin Clevett kzbin.info/www/bejne/oJK3iICLqrmKpKs&ab_channel=RobinClevette and to me it appears he does mention an air gap but then pushes the PIR quite a way into rafters leaving a gap at the front. He then goes over that horizontally meaning there must be a gap between the 2 lots of PIR. I'm not asking you to bad mouth his work as I like that he went to all the trouble of making jigs and using that special tape, just trying to understand.

[@SteveRoofer]

His video is not actually about the ventilation although he mentions it hopefully he will do through ventilation as regards more layers of insulation that's also acceptable as long as they are tightly secured together and that all of it is nicely secured with the appropriate through ventilation on the cold side of the roof

[@philsims6607]

@@SteveRoofer ok thanks 👍

[@allanhundeby1675]

Backward and forward. Backward and forward.