Garage Conversion - Is this correct?

[TwoByFour]

Hi all, new here and hoping to get some advice. I have builders doing a garage conversion for me but they way they are doing the walls is new to me and I want to make sure it's correct and they aren't taking shortcuts.

I have a single brick attached garage. In normal garage conversions I've seen them baton the brick walls, fill with insulation and plasterboard over it. My builders are putting thermal blocks against the existing brick walls and then will attach plasterboard over the thermal blocks (dot and dab maybe?).

Now I'm no expert so I don't want to challenge them without getting my facts right so is what they are doing ok? They've only done one wall so far so I have time to get them to stop and redo it the way I want/the way it should be.

Thanks in advance!

 

[jeds]

Thermal blocks on their own won't be sufficient in terms of insulation value. They might be planning to fix insulated plasterboard to the new blocks - which might be ok. Are there any plans for this conversion? Who is supervising the builders? What are they building the new blocks off of? Has the building inspector visited yet - maybe ask them what they think?

 

[TwoByFour]

Thanks for the reply. Yes they mentioned insulated plasterboard over the blocks. There are plans and we have a building inspector but he hasn't visited since the work started. The new blocks are ready made, grey looking with squiggly lines on them! Maybe I'll get the builders to stop temporarily and get the inspector in.

So do you think it's ok to convert the garage in this fashion as long as it's done correctly? I'm worried about damp/coldness as the new room will be used as a guest bedroom.

 

[garyo]

Are they leaving a cavity between the thermal blocks and the single skin?

 

[TwoByFour]

Yes, but it's only 15mm or so. Is that enough?

 

[jeds]

It's a fairly good method providing the insulated plasterboard is sufficient to meet thermal requirements. You could argue better than board on battens. It doesn't sound like they are doing anything wrong so I wouldn't stop them working. Maybe give the BCO a call and have a chat just for peace of mind. You've got plans - do they not specify how the walls are to be treated? Also, what's the plan for floor insulation?

PS, forget the 15mm cavity - that's just the natural mortar joint between brick and new block.

 

[TwoByFour]

I didn't see anything on the plans but I'll have to double check in case I missed it. I will make sure they use decent thermal boards and even double up if necessary. I will get the BCO to come on site next week, got some other things to discuss anyway so will bring it up then.

EDIT: Forgot to add info about the floor. It's being built up on a frame to level match the existing house floor level. It will be filled with insulation and then ply boarded from my understanding.

Thanks again for all the replies so far.

 

[^woody^]

With blocks and insulated plasterboard or whatever, you are losing at least 50mm off the width of the narrow garage, which you would not have done if the insulation was applied direct to the wall, or an insulated frame built.

So in that context its not the best way to convert the garage.

 

[TwoByFour]

Should have mentioned it's a big garage so width is not an issue but I can see your point.

 

[^woody^]

Perhaps building a wall off a floor slab and not direct off the foundation might be an issue?

 

[TwoByFour]

Good point, hadn't thought of that. What kind of issues might that cause? Are garages built on proper foundations (maybe a stupid question!)?

 

[tony1851]

The garage floor itself - which they are building off - will just be a slab of concrete anything from 75mm thick upwards.
Whatever thickness and quality it is, whether it would be OK to support the wall is a moot point, though aac block walls are not particularly heavy.

 

[theprinceofdarkness]

With a 15mm cavity you are relying on the bricky not to drop any mortar down it! Any that gets down it will bridge the cavity and cause damp. The inner skin must have a parging coat on it otherwise any mouse holes will cause air movement which will degrade the insulation. Likewise the inner plasterboard and its insulation must have air tight joints and not rely on a great dollop of plaster to hide gaps.
Somewhere you must have a VCL (vapour Control layer - thin plastic sheeting), this is to stop humid air from the inside getting into the insulation and condensing as it cools down Thus producing real water which will drip down and soak into your blocks.
Frank

 

[^woody^]

15mm is the collar joint, not a cavity.