Ask a tradesman

Conversions - General

Insulation in garage conversion

Hi, advice appreciated. I’m self managing the conversion of my garage, and have notified the council Building Control.
The garage (and house) are constructed with double brick, no cavity. I’m lining the roof with 100mm Kingspan leaving a 50mm gap, and then boarding over. The walls I propose to line with 50mm Kingspan, and the floor to lay DPD, then 75mm Kingspan, add another membrane then level above that with plain sand and lay a timber floor. Are there any issues with what I propose? Advice very much appreciated!

4 Answers from MyBuilder Conversion Specialists

Best Answer

Ok so it sounds like you have 9 inch brickwork, the main thing about garage conversions are the u values for a habitable space. Also making sure that damp from exterior walls does not penetrate to internal walls. here is how we would do it hope this helps. The insulation in the ceiling will depend on the size rafters if you have a flat. For flat roof you will need to add as much insulation as possible leaving min 30mm gap above, it would be wise to add some sort of ventilation to the cold side through soffit vents etc. For a pitched roof you can add 100mm loft insulation between raftes then 200mm loft insulation across the rafters on top.
So depending on the roof insulation if flat you will need to have u values calculated to upgrade the rest of the area lets say they would require 90mm cellotex in walls 75mm in floor.
What is always best is that you build a room within a room. We generally build stud walls leaving 30mm gap from inside of the wall, add a breathable membrane to the back side of the wall insulate between studs the required thickness for u values of insulation. Either use a plastic vapour barrier to warm side or aluminium tape joints for vapour barrier.
Floor it depends on height to Existing DPC personally we always prefer to screed the floor, you will need minimum 150mm from existing slab to existing dpc.If you have it add 1200gauge dpm making sure it turns up the wall atleast past existing dpc level. Floor will be the first part of the job you do, so if you are going to stud internally as mentioned above we always run a course of bricks or blocks to sit stud work on this is important, run the dpm up and over the new brick work to dpc height, add dpc and link both dpc and dpm, run another course of bricks on top. This final course of bricks will enable you to fix studwork without breaking the damp. then lay your 75mm insulation on top and then lay either vapour barrier or another 1200 g dpm over the insulation to prevent insulation being effected by the sand cement screed.
If you do not have the room then i would suggest a floating floor using 22mm tand G.
Thats is palster board plaster away you go


Answered 16th Jan 2020

I would advise you have a architect draw up a specification report first as building regs won't sign off if you have any issues later and it be costly for you if that is the case.


Answered 15th Jan 2020

I do not think that your work will pass insulation values and the sand barrier doesn’t sound too good need diagrams to advice further


Answered 15th Jan 2020

After carefully reading some of the questions are correct that have not followed the right order me personally would never suggest a customer to carry out professional work as it is very important to build the project by building regs and To follow protocol Also he Needs to get planes drawn up and submitted to the building office also don't think any builders should be telling a customer the way to build Anything Conversion or extension


Answered 26th Jan 2020

Post your job to find high quality tradesmen and get free quotes

Can’t find an answer? Ask a new question

Question Categories