Stud wall against roof - location and insulation

[AlanUK]

Stud wall between joists

I have a detached garage with room above, and I’m splitting the room into two, with a stud wall.  I want to place it running midway between two joists, running parallel with them – see the picture.  I will put noggins ever 400mm under the wooden floor between the pair of joists for the stud wall base to go onto.  Would this be ok?

 

For the walls and ceiling, can I just do the same, with small noggins?  Also, the insulation that is to go into the roof, would it sit behind the noggins, running the full length, or would I cut up small pieces of insulation to put between the noggins?  See my terrible drawing, showing a section through the room. Would the insulation run behind the smaller noggins (as shown in the black hatched option) or would it sit between noggins, as shown in the red hatched option?

Thanks,

Alan

[nod]

Yes nogs under the sole plate

Your easy way for the underside of the slope would be to counter baton with 75x25 mi This will give you fixing for stud and PB and leav a void for insulation 

[AlanUK]

44 minutes ago, nod said:

Yes nogs under the sole plate

Your easy way for the underside of the slope would be to counter baton with 75x25 mi This will give you fixing for stud and PB and leav a void for insulation 

 

Thanks nod.  Silly question - When you say "counter baton", do you mean laying the boards out horizontally across the joists?  I think I will need to do that anyways, to make up the depth of the diagonal boards that are stiffening the rafters together, so yes, that would work.

[nod]

1 hour ago, AlanUK said:

 

Thanks nod.  Silly question - When you say "counter baton", do you mean laying the boards out horizontally across the joists?  I think I will need to do that anyways, to make up the depth of the diagonal boards that are stiffening the rafters together, so yes, that would work.

Yes I do 

You may find that you have do this twice Once to take you flush with the bracing Then the next will allow you to set out at 600 centers 

But I would get all your 70 mil kingspan in first 

[AlanUK]

25 minutes ago, nod said:

Yes I do 

You may find that you have do this twice Once to take you flush with the bracing Then the next will allow you to set out at 600 centers 

But I would get all your 70 mil kingspan in first 

Good. I hope only to do it once, otherwise the room will get too narrow.  Is 70mm a mandated depth of insulation?

My builder said I need to put 25mm insulation boards over the bracing too. But I don't know if it's a requirement.

[nod]

No that’s not enough 

We normally use 70 between the rafter 30 mil air gap at the top 

and a minimum of 38 mil insulated backed plasterboard or 48 mil PB

Check with building control 

[Temp]

What are the rooms going to be used for? If these are going to be habitable rooms the whole thing needs to be properly  designed to meet building regulations, particularly  with regards to escape from fire.  

[tonyshouse]

Insulation between noggins and above them, leave 50mm ventilation gap but add as much insulation as you can 

 

for me nogs at 1200cc or two per run 

 

floor needs insulating and whole thing a vapour barrier and air tightness layer 

 

 

[AlanUK]

1 hour ago, Temp said:

What are the rooms going to be used for? If these are going to be habitable rooms the whole thing needs to be properly  designed to meet building regulations, particularly  with regards to escape from fire.  

It's a detached garage, and the room above will be an office. It' won't be used to live in.  Does that make a difference to the regs that I need to meet?

 

1 hour ago, tonyshouse said:

Insulation between noggins and above them, leave 50mm ventilation gap but add as much insulation as you can 

 

for me nogs at 1200cc or two per run 

 

floor needs insulating and whole thing a vapour barrier and air tightness layer 

 

 

Another silly question -  Why is a vapour barrier needed?  Are you talking about under the floor?  The ceiling below (i;e. the garage ceiling) will be covered in fire proof plaster boards - there's no risk of moisture coming up through the floor (unless there's something I'm missing here)

[tonyshouse]

Basics are that moisture moves from areas of high partial vapour pressure to places where it is lower, a downhill unstoppable process

 

lived in generally has higher pvp than not lived in - ie garage ceiling will get damp possibly grow mildew on top surface in winter 

 

vapour barrier will mitigate the risk 

[AlanUK]

Ah ok - and would I put that under the Redwood floorboards, or above the ceiling plasterboard  of the floor below?

[Temp]

6 hours ago, AlanUK said:

It's a detached garage, and the room above will be an office. It' won't be used to live in.  Does that make a difference to the regs that I need to meet?

 

I don't think a home office is considered a "habitable space" but the work is probably a "material alteration".

 

https://www.planningportal.co.uk/info/200130/common_projects/25/garage_conversion/2

The conversion of a garage, or part of a garage, into habitable space will normally require approval under the Building Regulations.

 

https://www.planningportal.co.uk/info/200130/common_projects/56/working_from_home/2

However, if your proposed project involves work which will affect the structure of the building, the means of escape and other fire precautions, or affect the access to and use of buildings, the regulations will regard your work as a 'material alteration' (and therefore 'Building Work') which must then comply with the regulations.

 

 

 

 

 

 

[tonyshouse]

Vapour barriers always go on the warm side of the insulation 

[tonyshouse]

Under or over the floorboards 

[AlanUK]

3 hours ago, tonyshouse said:

Under or over the floorboards 

Thanks Tony.  I'll discuss it with the building regs guys.