Alternatives to PIR for internal timber frame?

[idontknowwhatiamdoing]

Started framing one room and thinking about insulation inside.

I want to go with PIR but the cost and wait times are putting me off.

The frame construction is 100mm deep and is surrounded by a aircrete / breeze block cavity wall outer shell. There is a 50mm airgap between the inner and outer wall for ventilation

Interested to know what people have tried as an alternative to PIR, or is it a case of just bite the bullet and accept PIR is the only versatile solution currently in the UK?

 

 

[Iceverge]

Mineral wool.

 

Eps beads. 

[Thorfun]

it all depends on what U-value you want to achieve. if you can decide on that then you can choose a material that, at 100mm, will achieve that level.

[idontknowwhatiamdoing]

I basically want to achieve a warmer home than what it was before, which was just cavity walls and 50mm insulation (built in the 70s)

[Thorfun]

Just now, idontknowwhatiamdoing said:

I basically want to achieve a warmer home than what it was before, which was just cavity walls and 50mm insulation (built in the 70s)

and what was the 50mm insulation that was there before? PIR or something else? if it was PIR then 100mm of mineral wool won't give you much of an increase in insulation value.

 

you can use online U-value calculators like this one to help calculate it. 

 

https://www.changeplan.co.uk/u_value_calculator.php

[idontknowwhatiamdoing]

It was built in the 70s so it was fiberglass wool, which was damp and shrunk.

[Thorfun]

11 minutes ago, idontknowwhatiamdoing said:

It was built in the 70s so it was fiberglass wool, which was damp and shrunk.

ok, so then 100mm of glass mineral wool will most likely more than double the previous insulation levels. you can get 0.035W/m.K or 0.032W/m.K glass wool in batts format at a relevant thickness (Isover do a 50mm or 90mm 0.032W/m.K batt https://insulation-uk.com/products/isover-timber-frame-batt-32).

 

PIR has a thermal conductivity of 0.022W/m.K so 100mm of that will give you a much warmer house.

[Iceverge]

I wouldn't bend over backwards with thermal conductivity values. The actual quality of install is more important. To get PIR exactly correct is very tricky. It's only performs to its stated K value under lab conditions.  Also it's very expensive compared to mineral wool and EPS. 

 

I would get the the existing mineral wool vacuumed out of the walls. Then blow in EPS beads. 

 

Put an airtight membrane inside your framing, seal it to all windows and the floor and ceiling. Blow EPS beads behind.  Insulate the service cavity with mineral wool. Then plasterboard. 

 

Over all U value of about 0.25 at a guess. It would lightly perform much closer to this rather that PIR between studs. 

[Iceverge]

 

Actually I've underestimated it. This is the result for 63mm studs. 

 

If you want to minimize wall thickness omit the 45mm service cavity and include a 22mm strapping instead.