Garage conversion question

[Relent]

Hi all,

Long time lurker (diy'er) who uses the vast amount of knowledge on here to carry out tasks - thank you!

I have looked at posts on garage conversions but couldn't see any direct answers to my questions, so thought I would drop a message to see if anyone could offer some pointers.

I am doing a DIY half garage conversion. I have had competent traders in to do the gas (move pipework outside), electrics and cut the doorway/window openings.
I will be doing the stud wall between the garage space and new room space and flooring.

My question is about the above- stud wall, battens on the internal blocks for plasterboard and flooring.
Is it ok to batten the walls and erect the studwall to the concrete floor (with DPM) and then lay the timber floor joists up to the battens or stud.
Or should the floor joists be put down first so they are flush to the walls then install studwall on to the joists?

And second question, as I am battening on to the blocks wall for the plasterboard, do I need to fill the cavity between plasterboard and inner block?
The external wall is block and brick with cavity.


Apologies for the amateur questions.

(I have got a BCO but won't be able to ask until Tuesday now because of the bank holiday. I wanted to start getting the stud walls in position over the weekend as I will have some time)

 

[Bonni]

If you convert a garage into a living space, if it's attached to the house, you need building regs,

A concrete block, cavity, and brick outer wall would normally have 60mm Kingspan insulation. Medium density blocks would have 50mm. Floors would have 100mm.

So yes, put kingspan between the studs relevant to the construction of the walls, more the better.

 

[jeds]

Personally I would put the floor down first and work everything else off that. Although, if detailed correctly, it could be done the other way around. Your main issue is going to be getting the levels of insulation right and detailing of the layers. As a rough guide, for wall lining and stud partition, you will need a minimum of 100mm PIR insulation to reach regulations. But, these things are partially negotiable depending on the situation and you might be able to get away with less. But, to be safe, you'll need to agree that with your inspector before committing.

 

[Relent]

If you convert a garage into a living space, if it's attached to the house, you need building regs,

A concrete block, cavity, and brick outer wall would normally have 60mm Kingspan insulation. Medium density blocks would have 50mm. Floors would have 100mm.

So yes, put kingspan between the studs relevant to the construction of the walls, more the better.

Thank you.

I have got building control (private company) doing the regs.

For the stud wall between living space and the garage I am planning 100mm PIR. Same for the floor between the joists.

 

[Relent]

Personally I would put the floor down first and work everything else off that. Although, if detailed correctly, it could be done the other way around. Your main issue is going to be getting the levels of insulation right and detailing of the layers. As a rough guide, for wall lining and stud partition, you will need a minimum of 100mm PIR insulation to reach regulations. But, these things are partially negotiable depending on the situation and you might be able to get away with less. But, to be safe, you'll need to agree that with your inspector before committing.

Thank you.

For the stud wall I do plan 100mm PIR boards.

I am thinking about where I batten the block walls - will I need it there? I have read about vapour control to prevent wood rotting, but this is what I couldn't determine from what I have read.

I think you are right on agreeing with the BCO. Which now you have mentioned it, I can do the battens anyway as they will inspect before I plasterboard over so can put in the PIR at that point.
It would still be good to know if it is required so I can calculate the cost of buying more PIR.

This then comes to the floor.

I would like to batten the garage walls and build the studs to the current concrete floor, then build the floor framework inside that afterwards, again leaving open so inspector can see where I will fill the floor with PIR.
It doesn't sound like doing it this way round is a problem, but any advice is greatly appreciated?

 

[noseall]

For the stud wall between living space and the garage I am planning 100mm PIR. Same for the floor between the joists.

You will need a further say 50mm across the studs (as well as between) also. We use fire rated plasterboards on the garage side.

 

[noseall]

My question is about the above- stud wall, battens on the internal blocks for plasterboard and flooring.
Is it ok to batten the walls and erect the studwall to the concrete floor (with DPM) and then lay the timber floor joists up to the battens or stud.
Or should the floor joists be put down first so they are flush to the walls then install studwall on to the joists?

Wall first so that you have (vertical) continuity on the garage side.

 

[Relent]

Wall first so that you have (vertical) continuity on the garage side.

Great thanks, that is the way I'd prefer to do it.

I take it I can secure the Floor joists, which will be sat on the concrete floor, to the battens on the walls?

 

[Relent]

You will need a further say 50mm across the studs (as well as between) also. We use fire rated plasterboards on the garage side.

Is it ok to just put strips over the studs then fasten the plaster board through the PIR strips into the stud?

 

[noseall]

Is it ok to just put strips over the studs then fasten the plaster board through the PIR strips into the stud?

You could, but this won't satisfy reg's. In fact, since last June, the requirement is even greater.

Our last stud (garage) partition form inside to out...

12.5mm plain plasterboards, taped and skimmed.
18mm OSB (customer wanted to fix anywhere).
50mm Celotex across the studs, all joints foil taped
100mm studs with 100mm Celotex between, all joints foil taped.
Two layers of fireboards with joints staggered, taped and skimmed.

 

[Relent]

You could, but this won't satisfy reg's. In fact, since last June, the requirement is even greater.

Our last stud (garage) partition form inside to out...

12.5mm plain plasterboards, taped and skimmed.
18mm OSB (customer wanted to fix anywhere).
50mm Celotex across the studs, all joints foil taped
100mm studs with 100mm Celotex between, all joints foil taped.
Two layers of fireboards with joints staggered, taped and skimmed.

I can understand the 50mm over the studs to prevent thermal bridging through the timber.
Did you box in the studwork with 50mm then 100mm in the cavity?

Also, I though the objective was to reach a minimum thermal value.
Did the BCO calculate the thermal value of that, or did they just pluck it out of the air?

And what was the purpose of the OSB?

 

[noseall]

I can understand the 50mm over the studs to prevent thermal bridging through the timber.
Did you box in the studwork with 50mm then 100mm in the cavity?

Yeah. 50mm across with 100mm between.

Also, I though the objective was to reach a minimum thermal value.
Did the BCO calculate the thermal value of that, or did they just pluck it out of the air?

No. I just went on past experience (vaulted roofs etc). BC were happy though.

And what was the purpose of the OSB?

Just a fixing benefit for the customer. Nowt worse than trying to locate studs 3 months on.

 

[Relent]

Yeah. 50mm across with 100mm between.

No. I just went on past experience (vaulted roofs etc). BC were happy though.

Just a fixing benefit for the customer. Nowt worse than trying to locate studs 3 months on.

Thank you.

With the 50mm PIR around the stud, and the cavity filled with 100mm. Were you left with a 50mm void?

 

[noseall]

With the 50mm PIR around the stud, and the cavity filled with 100mm. Were you left with a 50mm void?

Across the stud, not just around. I.e. solid 50mm sheets covering the whole wall....

wall.jpg

• noseall
• 29 May 2023

 

[Relent]

Across the stud, not just around. I.e. solid 50mm sheets covering the whole wall....

wall.jpg

• noseall
• 29 May 2023

Thank you