Garden Room - Part 13 - PIR in Roof

Join me on my journey, building a garden room, cabin, man cave, glorified shed, whatever you wish to call it.
I'll be building from scratch, after years watching others on youtube with envy.
Garden Room Playlist - • Garden Room - Part 1 -...

[@grim-upnorth]

Some people have asked about the "cold roof" design and the fact I haven't left an air gap. So I'll pin this comment in the hopes it pre-emptively answers any similar questions. This room is sized and located deliberately so that it does not need to be governed by Building Regulations. (going into specifics is a whole video itself, and there are plenty already out there). Also, this is not a cold roof, it's a hybrid roof. Because the room is low occupancy, the amount of moisture in the air inside the room is much lower compared to a normal home where multiple people are respirating, boiling kettles, cooking, doing the dishes with hot water, having showers/baths and so on. The room will be occupied by 1 person most of the time, and only for a couple of hours per day. The windows have ventilation above the glazing, and the windows also open for further ventilation should it be required. There is a vapour barrier (not in this video) between the main part of the room and the airgap under the ventilation. Only a negligible amount of humid air will ever accumulate in that gap. But the air in that gap will always be at the ambient temperature of the rest of the room. Because the insulation is flush up against the roof boards, there is no (super negligible) air touching the "cold" boards, so there's no (super negligible) chance of condensation. This roof method has been used by very experienced professional garden room builders for many many years, as it allows you to gain some extra internal head room if you're building within the rules of Permitted Development (England). I hope this helps, and thank you all so much for watching my videos 🙂

[@paulrobinson3042]

Just get a Festool insulation saw and dust extractor, No dust

[@grim-upnorth]

Absolutely! I'll buy the Festool saw then not have enough money left to buy the insulation I need to cut haha. Seriously though, you're right. There's always the correct tool for the job and if I were to be doing this on a regular basis, or to make a living, I would 100% buy the festool cutter. But this is the one and only time I plan on using PIR for anything, I'm a DIYer and have had to build this whole thing on a very tight budget. 🙂 Thanks for watching

[@robertferguson4607]

Are you not supposed to leave some ventilation between the top of the insulation and the bottom of the roof boards?

[@grim-upnorth]

In the case of a standard cold roof, yes you're absolutely correct, and you'd have to used vented soffits front and rear to allow for airflow, so moisture can escape. However, because this building doesn't fall under building regs, and I'm limited to 2.5m in height. It's relatively accepted that it's possible to use this method (in the video) to gain a few inches of internal head room. It's a low occupancy structure, i.e. only 1 or 2 people will be in there at a time, and for relatively short periods of time. Basically, it's not a house with multiple people, cooking, washing, breathing and so on, that would cause humidity in the structure. It's called a hybrid roof (neither warm nor cold roof) and a few expert garden room builders swear by it, for the extra head room you can eek out of permitted development builds. Thanks 🙂

[@101projects2]

You hate pir...and I have a garage full of it ready to insulate my workshop 😅 Not looking forward to that. Enjoying the series Can't wait to see it when it's all finished 👍 ...one question are you not supposed to leave an air gap between the pir and the underside of the roof (cold roof) ? I'm no expert though.

[@grim-upnorth]

Brilliant, thanks for watching.The biggest problem for me was the dust and bobbles getting into my eyes. No matter what eye protection I used, I struggled. So I eventually just didnt' wear any as it made no difference. Safety specs - the dust gets round the back of the lenses and into your eyes. Goggles - they steamed up to the point I couldn't see. If you can figure out a way to protect your eyes and still see what you're doing, you'll be fine honest. It's not that bad to work with, just the dust is horrible (and a pain to clean up afterwards) Re: air-gap. see my pinned comment

[@101projects2]

​​​@@grim-upnorth Ref the air gap, I get what you're saying now you've explained it, it's not like it's going to be air tight the reality is, almost regardless of the amount of insulation you install the building by the very natural of the structure and materials used is going to have natural ventilation to a degree and thermal bridging, it will definitely give you the desired effect of making it feel warmer than outside (or cooler) but relatively speaking (when compared to a house or extension for example) the thermal effectively won't be great so damp and moisture buildup is unlikely.

[@grim-upnorth]

@@101projects2 Exactly, its nice having such a considered and understanding response, thank you. I've seen people in other places get all narky about it, usually professional tradespeople who build actual houses etc. saying its wrong. And I agree, if this was required to hit building regs and was part of my home, or if this was a living quarters with bathroom/mini kitchen annex sort of thing... but it isn't. The reality is I will be in this room, playing games on my computer, or watching TV, for at most 4 hours per day... it's not going to be lived or slept in. 🙂

[@101projects2]

​@@grim-upnorthno probs, it'll work out just fine 👍 I'm about 2 months behind you, fighting off the open bare carcass of my workshop build from the elements, I'm constantly checking the weather hoping it won't rain before I can get it water tight.

[@grim-upnorth]

@@101projects2 yep, this was me a month or so ago, when we had that horrid few weeks of weather. floor got water damaged, edges of the OSB swelled up. I've had to sand them down since getting the roof up 😞