Insulation

[Thomo39]

Morning.
I've studded out my external garage and have a void of 230mm between the stud and the external brick..
I currently have 100mm kingspan in the stud.
Is it ok to leave a gap of 130mm between the external brick and the kingspan or does it need to be filled and leave a smaller gap?
Cheers

 

[tomfe]

Yes, but why have you left so much space?
Would you not rather have and extra 100mm of space at each wall?

 

[Thomo39]

It's only 3 meters squared. The back walls only have a void of 100mm its down the side walls where the void is 230mm..the reason being is there are 3 brick collums down each side wall so rather than stud round each collums I decided to just run my track straight down..
Do you suggest that the fill 230mm void is filled or can I leave a smaller gap ? I was thinking another 100mm kingspan would suffice

 

[tomfe]

You can fill it and leave small gap, 25mm if rendered or 50mm if not would be best, or leave it. 100mm is enough for building regs 0.28w/m²k

 

[John D v2.0]

That gap is fine but it will be very cold and liable to condensation unless it's well ventilated/drained. Also you could have saved a lot of cash by using wool instead of king span.

 

[Thomo39]

That gap is fine but it will be very cold and liable to condensation unless it's well ventilated/drained. Also you could have saved a lot of cash by using wool instead of king span.

I got the kingspan free I would have used will roll if I didn't.
I'm going to put a 4 inch fan in the ceiling void so that will help

 

[^woody^]

I'm going to put a 4 inch fan in the ceiling void so that will help

Will help what?

 

[rssteve]

Help condensation occur in the ceiling void by the sounds of it.

 

[tomfe]

That gap is fine but it will be very cold and liable to condensation

Why?
What's the difference between leaving a 50mm gap and a 200mm gap?

 

[John D v2.0]

Why?
What's the difference between leaving a 50mm gap and a 200mm gap?

About 150mm
But in all seriousness there's not much difference, if the gap is cold it need ventilating. If it's room temperature it needs to be not ventilated!
You could plug in a condensation risk analysis and find out for sure based on u values and permeable layers, but in general the more insulation you have the worse the risk.

Edit: having read the thread again you're assuming the inside of the wall is already drained to outside like a cavity wall and I'm not. Not sure which is the case.

 

[tomfe]

the wall is already drained to outside like a cavity wall and I'm not.

Do you add weep holes for the reason of condensation?

 

[John D v2.0]

Do you add weep holes for the reason of condensation?

Personally no but I'm not a builder. The normal way of building a cavity wall with insulation would be fine. The normal way of cladding leaves a gap that is drained via gravity.
I guess what you're saying is how can I know that the permeability of the existing walls is low enough to have condensation build up that might harm the structure, but as above you'd have to do a condensation risk analysis to be sure.

 

[tomfe]

As long as you have a vapour check on the warm side you should have no problem with condensation.

The normal way of building a cavity wall with insulation would be fine. The normal way of cladding leaves a gap that is drained via gravity.

Weep holes are added not for condensation but for penetrating damp through the outer skin same with cladding. With timber cladding the vented void is also not for condensation but to allow the cladding to dry out.

My point was you are saying a 50mm cavity will not allow condensation to form yet a 150mm cavity will. How does that work?

 

[John D v2.0]

As long as you have a vapour check on the warm side you should have no problem with condensation.

Weep holes are added not for condensation but for penetrating damp through the outer skin same with cladding. With timber cladding the vented void is also not for condensation but to allow the cladding to dry out.

My point was you are saying a 50mm cavity will not allow condensation to form yet a 150mm cavity will. How does that work?

Fair enough I think we're basically on the same page! The only thing I'm not sure is all this about the size of the gap, I don't think it really would make a difference and I didn't intend to say it would! So scratch that out wherever it is