Converting detached garage/workshop

[vtyr]

Hello! Long time lurker here.

I'm currently planning to convert my external workshop (approx 60sqm) to WFH offices. At the moment, it's got a roller garage door, uPVC windows + door, filled block and brick cavity wall and a pitched trussed roof with no loft insulation. I'm currently having air conditioning installed as a means of heating the area (I plan to erect 2x offices, 1 main area, it already has a w/c), and as such the heating engineers have spec'd out a 3x internal and bosch 5000i external unit.

My question arises here. I've done endless research into this, and I'm trying to work out the best way to improve the thermal efficiency of the building. I'm going to be adding 300mm loft insulation, changing the garage roller door to a triple glazed sliding door, but i'm unsure of what to do about the walls. I've been thinking of going for 50x75mm CLS studs (63mm finished) and 60mm Rockwool RWA45, followed by a vapour barrier and then plasterboard. I'd welcome any thoughts on this - Rockwool rather than PIR to keep the cost down, and surely this will be better than dot'n'dab anyway? So my wall make-up:

- Block and Brick wall with 80mm blown-in insulation cavity
- 50x76mm CLS studs secured to the wall
- 60mm Rockwool RWA45 between Studs
- 1200 gauge vapour barrier
- 12.5mm plasterboard

Also... bonus question... the floor is currently concrete slab, followed by 40mm (or so) polystyrene and then 18mm T&G P5 chipboard. I'm thinking of changing this out to also improve thermal efficiency, as it's been cut up in a few places so want to also avoid the dreaded creakyness of poorly maintained T&G if possible (my entire house has T&G which was ripped up when CH was installed 20yr ago, before I moved in). ANy ideas on best action here? Thinking Concrete Slab -> DPM -> PIR -> Engineered wood floor

Thanks!

 

[23vc]

Rwa45’s branded as acoustic insulation, I haven’t checked the figures but not sure how much bang for buck it gives for thermal. I’d compare its u value to things like cavity batts of similar thickness if you don’t want to go PIR.

 

[vtyr]

Rwa45’s branded as acoustic insulation, I haven’t checked the figures but not sure how much bang for buck it gives for thermal. I’d compare its u value to things like cavity batts of similar thickness if you don’t want to go PIR.

The whole "acoustic/sound" thing has been puzzling me. Most of the Rockwool stuff appears to be marketed as such, yet produces 0.034W/mK at 60mm thickness versus 0.037W/mK of 50mm thick Knauf Cavity Wool slab

 

[noseall]

Hello! Long time lurker here.

I'm currently planning to convert my external workshop (approx 60sqm) to WFH offices. At the moment, it's got a roller garage door, uPVC windows + door, filled block and brick cavity wall and a pitched trussed roof with no loft insulation. I'm currently having air conditioning installed as a means of heating the area (I plan to erect 2x offices, 1 main area, it already has a w/c), and as such the heating engineers have spec'd out a 3x internal and bosch 5000i external unit.

My question arises here. I've done endless research into this, and I'm trying to work out the best way to improve the thermal efficiency of the building. I'm going to be adding 300mm loft insulation, changing the garage roller door to a triple glazed sliding door, but i'm unsure of what to do about the walls. I've been thinking of going for 50x75mm CLS studs (63mm finished) and 60mm Rockwool RWA45, followed by a vapour barrier and then plasterboard. I'd welcome any thoughts on this - Rockwool rather than PIR to keep the cost down, and surely this will be better than dot'n'dab anyway? So my wall make-up:

- Block and Brick wall with 80mm blown-in insulation cavity
- 50x76mm CLS studs secured to the wall
- 60mm Rockwool RWA45 between Studs
- 1200 gauge vapour barrier
- 12.5mm plasterboard

Also... bonus question... the floor is currently concrete slab, followed by 40mm (or so) polystyrene and then 18mm T&G P5 chipboard. I'm thinking of changing this out to also improve thermal efficiency, as it's been cut up in a few places so want to also avoid the dreaded creakyness of poorly maintained T&G if possible (my entire house has T&G which was ripped up when CH was installed 20yr ago, before I moved in). ANy ideas on best action here? Thinking Concrete Slab -> DPM -> PIR -> Engineered wood floor

Thanks!

We tend to trap say 50mm PIR against the wall with a slim stud i.e. 50mm x 50mm, so that the insulation is continuous and the studs are protected from shadowing by the continuous insulation.

 

[vtyr]

We tend to trap say 50mm PIR against the wall with a slim stud i.e. 50mm x 50mm, so that the insulation is continuous and the studs are protected from shadowing by the continuous insulation.

Thanks. Would you be able to let me know the most affordable (slimline under 100mm) wall make up that sits within renovation building regs, taking into account the cavity wall with fill?

 

[noseall]

Thanks. Would you be able to let me know the most affordable (slimline under 100mm) wall make up that sits within renovation building regs, taking into account the cavity wall with fill?

Bulky = cheap.
Slimline = expensive.
I'd probably look at trapping 25mm PIR against the wall using 25mm x 50mm roofing battens, screwed through (long screws), into the wall. Then fit another 25mm PIR between, then board.

 

[big-all]

my friend installed 3" rockwool all surfaces i walked past the back off his garden room down an alleyway so 6 ft away with a 6ft fence panel to the room back i was talking normally and he could hear me clearly

 

[vtyr]

my friend installed 3" rockwool all surfaces i walked past the back off his garden room down an alleyway so 6 ft away with a 6ft fence panel to the room back i was talking normally and he could hear me clearly

Interesting, was it warm though? I'm only looking for thermal efficiency here, as the building is block and brick cavity.

 

[big-all]

Interesting, was it warm though? I'm only looking for thermal efficiency here, as the building is block and brick cavity.

yes as far as i know 'i did ask him some months later iff he was happy with it and him being a grumpy sod if things go wrong he would have moaned but he didnt
but he wasnt happy as he wanted to practice his drums in there

 

[vtyr]

So I think I'm going to go with either of these two options, and whilst PIR doesn't necessarily(?) need a DPM, I'm wanting to be on the side of caution, and thinking of also expanding foam the edges if it's not cut perfectly. Also will look to use foil tape around the cuts/edges of the PIR. Am I on the right lines here? Option 1 or 2? 1 is preferred for the service void/backboxes etc.

Though I did speak to building control, who said the U Value of a renovation cavity wall only needs to meet 0.55u versus 0.18u of a new built cavity wall, and this wall likely already meets it without the stud/PIR work - but he also said insulation is the best investment, and there's a stark difference between "what the minimum building regs are, and what you'd be happy living in".

Alternatively, like @noseall mentioned, sticking the PIR between the inner blockwork and studs, and then DPM across the face of that and the studs might be preferrable?