kingspan quiery

[John1954]

I am thinking of building over my garage to create a larger bedroom. I have had discussions with builders ,of how to achieve the 100mm cavity for the room above, as there is a very small cavity on the garage of about 25mm to 50mm.One builder suggested that a trench is dug around the internal garage walls to expose the foundations then this be filled with concrete, then another internal skin built and attached to the existing thermalite skin, this would then give the 100mm cavity for the bedroom. But this would cost between £1000 and £2000, a significant amount.Then I had another builder suggest building up on the existing walls ie with only the small cavity. and then putting the insulated plasterboard KINGSPAN 100mm on the walls. But he wasn't sure if this would be allowed on my property as it was only built 2001. He wasn't sure about the building regs with this and could it only be used on older properties with little or no cavity.
I would be grateful for anybodys thoughts on this..

 

[jeds]

You could build up with minimal cavity and insulate internally. I've also sometimes used a timber frame in this situation. The frame sits in the floor joists.

 

[freddiemercurystwin]

Lots of ways to do it really, for this I think you would be advised to get someone to do some regs drawings for you, you will very likely need to get a structural engineer in to sort the structure out too.

This is just one way to do it:

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• freddiemercurystwin
• 1 Feb 2011
• 3

 

[John1954]

Many Thanks for all your replies, I will consider both options and discuss these with structural engineer.
John

 

[freddiemercurystwin]

The point is there is no one solution each job is different.

 

[John1954]

Hi , Yes I know what you mean, I just thought it was a bit extreme to go digging my garage floor up , and I knew there must be some other less labour intensive way to do it as you see extensions going up above garages fairly regulary. Although I think the solution in the drawings you kindly sent could well be on the same scale money wise, as I would have to dig out for the brick pillars. And would the internal wood stud frame be capable of supporting the roof because it normaly sits on the celcon .
Many thaNKS John

 

[freddiemercurystwin]

The design I posted utilised existing piers in the garage so no additional ground works were required. A timber frame inner skin is a standard method of construction and will easily support the roof. Single skin garages generally have existing piers especially when built in 2001, does you garage not have piers in the corners or elsewhere?

 

[freddiemercurystwin]

You may or may not find this thread useful, I started it, the detail posted above was how the design eventually ended up //www.diynot.com/forums/viewtopic.php?t=201599&start=0

There are dozens of threads on here on building a room above a garage, maybe have search.

 

[John1954]

Hi , No there isn't any brick piers , just celcon walls meeting at a right angle, because this is what I said to the builder when he came That I thought they could put in RSJs and build off them but he said he would have to build in piers for support so it still required to be dug and then there would be the cost of the beams so it was a case of swings and roundabouts.
John

 

[jeds]

If I read right your garage is double skin wall. So all you need to is something like this:

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• jeds
• 4 Feb 2012
• 1

 

[freddiemercurystwin]

Aye, this thread won't really go anywhere until you can confirm what the walls are, single skin or double skin like jeds drawing above or cavity walls or what?

 

[John1954]

Hi I have only just got in been out all day so I have only just picked up your reply. The walls are an inner wall of celcon and about a 25mm cavity, no insulation then facing brick on outer skin.

 

[John1954]

Hi again If jeds drawing makes it that simple why would the builder not offer me this method, and would this method in your opinion be ok with building control.
If I don't respond to your reply immediatly I am not being ignorant I am just busy doing other jobs.

 

[jeds]

This method was used and passed by BC with no query. But you'd need calcs to show the loads and support are suitable. All situations will be slightly different.

 

[noseall]

Jeds' method and Freddies method have their advantages/pitfalls like all methods.

For example The timber stud would need to be erected first i.e. prior to the brickwork, so that sheathing ply and breather membrane can be fixed to the outer face prior to adding the external skin.

One one occasion the architect designed a 300mm steel plate that sat atop of a 275mm cavity wall so that the new walls above could be built wider forming a kind of steel corbel.

Believe me, sometimes it is simpler to dig down and build a new wall from scratch.