Insulation in Timber frame wall.

[Mike.Hen]

Hi, Im in the middle of doing my building warrant for a self build extension and have a query i hope someone can help me with. I need to achieve a u value of 0.22 for my walls. Ive used the online calculators and they are telling me i need 165mm minimum to achieve this. I am using 145mm timbers.

If i add a 25mm solid kingspan board on the outside of the timber and 140 between studs. Can this solid board be part of the cavity or do i need to increase my cavity gap to 75mm to keep the 50mm cavity between the timber frame and the outer block work.

Anybody know of a way to get 0.22 and keep the insulation between the studs.

Cheers

 

[cjard]

Please note this particular forum is for documenting(blogging) about long running projects, not for asking questions

Sounds like you're basing it on wool? Use kingspan and you can achieve .22 with either 80mm and a foil faced breather membrane or 100mm and a normal breather. Personally, I've a doubt that foilfaced breather is quite as significant as 20mm of PIR/PUR; but it's generally good for another .01

https://www.uvalue-calculator.co.uk/calculator/walls/timber frame/insulation between timber studs with (insulated) plasterboard/140mm/brick/standard/0/100/

As your studding is 140 but you only need around 100mm of kingspan feel free to take a look at secondsandco - you've got 40mm gap to play with so you can take a punt on boards that are tapered, warped etc

If you want to persist with wool you can look at lining the inside with insulation backed plasterboard, tip: its more cost effective to make your own

Thermalcalconline has a good calculator to specify custom wall buildups including bridges layers. Even takes nails into account. You might find that using eg 140 wool fill plus some EPS instead of PIR gets you to .22 and is cheaper. What you doing for air tightness?

I bought an old school table saw and fitted a 14 inch blade, could cut up to 160mm boards with it by running a single cut and snapping the rest. The raggy snapped part of the board did a good job of holding it in place between the studs. Cutting the board with a slight angle to the edge was another technique and made it easier to foam in- the widest part of the board (inserted first) was a couple of mm wider than the stud spacing and held the board in place, the narrower part formed a gap to foam up. Foam was soudal from eBay, about 2.50 a can, gun style

I used reflective breather, 140 PIR/PUR between the studs and 100mm over, then OSB, reflective sealed vapour barrier (air tightness) 25mm battens (service void) and plasterboard. All insulation was seconds grade kingspan and about a third the normal price, hence the overdose. Walls are about .12 I think. Long job; well sick of it by the end!