Garage conversion insulation

[gunnag]

IM in the process of converting an attached brick garage into a habitable space. A local builder has given me some ideas and we discussed how he would insulate the walls. His plan is to build a timber stud frame and fill the gaps with 50mm cellotex. The cellotex would be in direct contact with the brickwork with no cavity. The studwork would then be covered with plasterboard and skimmed. Since the garage is single skin brickwork, IM wondering whether this is the correct approach and whether a vapor barrier and/or a cavity should be used? When I questioned the builder he said there was no need for a vapor barier as the cellotex has a silver foil backing and is waterproof.

Thoughts and comments about this approach appreciated

 

[noseall]

Depending upon how you design it thermally, a typical section would be 105mm facing brick, 100mm studs, 100mm celotex between studs, 50mm across studs, 12.5mm duplex boards and skim.

Are you running this past building control?

 

[gunnag]

No, we are not running this past building control. Although I mentioned turning the garage into habitabile space, I dont mean as a bedroom or lounge, more likely as a utility room or workshop area.

My concern was whether condensation could form within this type of structure and if we should be using a vapor barrier. Indeed is this sufficient insulation to satisfy building regs?

IM interested in your comment

a typical section would be 105mm facing brick, 100mm studs, 100mm celotex between studs, 50mm across studs, 12.5mm duplex boards and skim.

.

What my builder is suggesting is 50mm of PIR foil lined celotex fitted inbetween 50mm studword with 12mm plasterboard ontop, no cavity. This is half of what you are suggesting so presumably less thermally efficient.

How does this fit with building regs? Thoughs and comments welcome.

 

[noseall]

50mm of foam board insulation will not conform. It is about a 1/3rd of the way there.

Furthermore, the project as a whole will not conform unless you are designing and building it as such.

For example, the floor, walls and roof (if applicable) would all need to conform.

As will any venting to the utility, the electrics, heating and any structural alterations.

It does not need to be a bedroom or a lounge to require building regulations.