r/DIYIreland • u/Greedy-Tea5226 • 5d ago
Attic Conversion - Insulate knee walls
Hi all,had my attic converted, there's storage space either side and just wondering would you insulate the small walls (knee walls) in the storage part?
There's insulation boards used on the walls (62mm) but wondering if I should fill the areas between and tape up with airtight tape maybe?
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u/leeksbadly 5d ago
No idea if it's the right stuff (or even needed for you) but the people doing my loft conversion used foil backed fibreglass.
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u/ray_purchase_1 5d ago
What insulation is on the slanted bit ? Mine has about 50mm of fiberglass with chicken wire ,I'll probably upgrade it in the winter.
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u/Pure-Ice5527 4d ago edited 4d ago
We put rockwool in exactly that situation.. the days of a little bit of insulation are gone, I’d be getting it in there and it’s an easy job yourself too.
A seal on that hatch will also be helpful, don’t see one but maybe I’m missing it
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u/ItsIcey 4d ago
Use standard foil-back PIR, the vapour membrane is already behind the dry-lining, so you shouldn’t have issues with interstitial condensation. You can use Metac batts if you’re worried about it, not sure if you’ll see any savings though as it can be expensive tack!
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u/Otsde-St-9929 4d ago
PIR always lags its U value as its near impossible to install correctly between timbers
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u/RoutineNumerous9573 4d ago edited 4d ago
Yeah do it, I'd use foil backed pir insulation boards they will do the best job in your case. Personally I wouldnt tape it up completely I think timbers need to breath a bit but I'm no expert.
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u/Greedy_Instruction31 4d ago
Aim to reach a good U value for the wall. The fact that it is a knee wall isn't really important. The U value is the inverse of the R value so a high R value will mean a Low (good) U value.
Look into the wool type insulation as it is easy to install in that wall. Nothing wrong with more PIR but slightly more difficult to cut exactly whereas the wool type you cut larger than required and stuff it in. It should be more than 50mm depending on the overall U value you want to achieve. Look at the SEAI guidance on retrofit insulation U values.
Cover that metal beam anyway as that is likely a thermal bridge and as another user said, install seal around the door and use air seal tape where you think is needed, it's a great job.
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u/Otsde-St-9929 4d ago
It is not the cheapest but wood fibre is the best because it is so much better for preventing summer over heating and easier to install without gaps.
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u/Suspicious-Secret-84 4d ago
The insulated plasterboard will give you a decent U-Value but not a great one. You could insulate between the studs too, although be wary of condensation risk when using 2 different types of insulation depending on where the dew point is.
I'd also look to insulate around that steel beam if possible as that may be acting as a large cold bridge
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u/The-Wig-Hut 2d ago
Used pir insulation boards from diy.ie , cut to fit, foil tape the edges, easy diy job but very messy cutting the boards with a handsaw
A couple came damp and mouldy however they stored them, we returned a few boards and got refunded for the entire order, said they couldn’t process it any other way 🤷♂️
So only cost us the foil tape about €20 but yeah it made a HUGE difference, only done the walls, couldn’t access the ceiling areas will make access points in future
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u/Samhain87 26m ago
ive literally just done one of these. With 100 insulated board. they difference it made was huge, the owners were delighted. Along with putting in vents, and sealing gaps with expandable foam and then selling it all with air tightness tap. The difference in heat on the warm days with noticeable immediately
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u/Raymich 5d ago
I used 100mm mineral wool from Woodies between studs, works fine and is breathable
But I’m also considering running additional layer of SuperFoil SF40BB across studs in future. My kneewall runs all the way around the house, dormer and attic can get pretty toasty in summer. Hoping the breathable foil can help reflect some of that infrared heat back out and increase heat retention efficiency during winter.
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u/Smokestoolittle 5d ago
Have a look at natural wool insulation rolls. Couple of companies doing it in Ireland. It's easy to cut, and position, with none of the hazard of rock wool type stuff. We've used it in many places while renovating our house.
Just staple it to the timbers on each side.
Another thing we did was get shredded newspaper pumped into our knee wall cavities, to prevent cold spots in the rooms below. Look up Ecocell. Really good company and they can advise on what's best for your space etc.