Garage conversion botched job
Discussion
Hi all
New member here hoping to get some advice on a botched garage conversion.
My builder converted part of garage into utility. This is 2.8m x 3m. The garage has a single skin external wall. He updated this wall with dot and dab xps insulated plasterboard Knauff 50mm. Building control say this is too thin. I am looking at a big job ripping this wall upgrade out and redoing with 100mm timber batten + cellotex insulation. Does anyone have a better solution? The build passes condensation analysis but works out to 0.65 u value.
To satisfy building control i need 0.35 max. Any pointers at all?
New member here hoping to get some advice on a botched garage conversion.
My builder converted part of garage into utility. This is 2.8m x 3m. The garage has a single skin external wall. He updated this wall with dot and dab xps insulated plasterboard Knauff 50mm. Building control say this is too thin. I am looking at a big job ripping this wall upgrade out and redoing with 100mm timber batten + cellotex insulation. Does anyone have a better solution? The build passes condensation analysis but works out to 0.65 u value.
To satisfy building control i need 0.35 max. Any pointers at all?
There are a couple of other routes to Building Regulations compliance that might offer you more flexibility:
1) The 'area weighted U-value' method, which allows you to offset the excessive heat loss from one element (the walls in your case) by reducing the heat loss from other elements (eg. by having less glazed area than you are allowed, and/or by improving the U-value of other elements - roof, floor, windows - beyond the normal minimum standards).
2) By running a SAP calculation, which takes into account not only the above factors, but also the efficiency of the heating system and (potentially) the airtightness of the building and solar gain.
A full SAP calculation would typically cost you ~£250, but it might avoid the need to do any physical work at all (or it might allow you to do something cheaper and simpler, like stuffing more insulation in the loft.
The lesson to be drawn is to get someone competent to design it before you build it, though.
1) The 'area weighted U-value' method, which allows you to offset the excessive heat loss from one element (the walls in your case) by reducing the heat loss from other elements (eg. by having less glazed area than you are allowed, and/or by improving the U-value of other elements - roof, floor, windows - beyond the normal minimum standards).
2) By running a SAP calculation, which takes into account not only the above factors, but also the efficiency of the heating system and (potentially) the airtightness of the building and solar gain.
A full SAP calculation would typically cost you ~£250, but it might avoid the need to do any physical work at all (or it might allow you to do something cheaper and simpler, like stuffing more insulation in the loft.
The lesson to be drawn is to get someone competent to design it before you build it, though.
Your builder is an idiot, I’m afraid. Current regs would need 150mm PIR (Celotex / Kingspan / Quinntherm etc). So that’s 6” x 2” stud work with PIR between, vapour control layer, plasterboard.
It’s possible you (he) could re-use the existing materials if it’s thought about carefully - 4”x2” studwork with 100mm PIR then the existing treatment on top of that.
It’s possible you (he) could re-use the existing materials if it’s thought about carefully - 4”x2” studwork with 100mm PIR then the existing treatment on top of that.
Thank you for the very useful pointers. I did have a design but forgot i need to check the builder is actually following it. They put this up in a day and I didn’t stay on ball.
Will this build cause problems down the line? I mean it maybe better to bite the bullet , rip it out and start again to do it properly? I did get knauff to do calculations and it said condenssation clears out in summer so guess technically i wont have an issue.
Will this build cause problems down the line? I mean it maybe better to bite the bullet , rip it out and start again to do it properly? I did get knauff to do calculations and it said condenssation clears out in summer so guess technically i wont have an issue.
PhilboSE said:
Your builder is an idiot, I’m afraid. Current regs would need 150mm PIR (Celotex / Kingspan / Quinntherm etc). So that’s 6” x 2” stud work with PIR between, vapour control layer, plasterboard.
It’s possible you (he) could re-use the existing materials if it’s thought about carefully - 4”x2” studwork with 100mm PIR then the existing treatment on top of that.
Agree - he is an idiot. The annoying thing is if he had used 100mm xps instead of 50mm then it would have met the u value reqs. It’s possible you (he) could re-use the existing materials if it’s thought about carefully - 4”x2” studwork with 100mm PIR then the existing treatment on top of that.
PhilboSE said:
Your builder is an idiot, I’m afraid. Current regs would need 150mm PIR (Celotex / Kingspan / Quinntherm etc). So that’s 6” x 2” stud work with PIR between, vapour control layer, plasterboard.
Actually, 67.5mm. of PIR is sufficient to meet the U-value currently required for extensions (U=0.28).You don't fix the insulation between the studs, and you don't need a VCL for this approach. You fix timber battens to the face of the brickwork, with a strip of DPC trapped between the stud and the brick, then you fix the insulated plasterboard to the battens. This avoids the thermal bridging caused by the studs themselves, and thus reduces the thickness of insulation required.
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