How to fix the external leaf.

[HWBT_sometimes]

Hi

My house has a ~2" cavity. The new extension has a 6" cavity. The inner leaf of the extension has been made with a wall starter on the house wall.
The external leaf on the extension basically touches the corner of the current house.

How can the the external leaf be fixed to the house please? Can i use a twisted bent restraint strap across the inside of the top course and attach to the house. What needs to be done to pass BC?

Thanks

 

[Ivor Windybottom]

The house and extension walls don't actually meet. Could it be built with a half-brick return on the end so it could attach to a wall starter? i.e. an extra half brick within the cavity, perhaps a half or even full brick in length.

Obviously this compromises the insulation. But so does the original house anyway. It would be far simpler if the outer skins aligned, but I guess you're already building it.

Have a discussion with BC before going ahead with anything. They definitely won't be happy with your bit of rusty metal idea!

 

[stevie888]

That's a weird detail TBH.

Have you had your drawings approved before you started?

If you are at this stage is your builder guilty of a setting out cockup?

 

[jj4091]

Is the outer skin already built? If so what materials have ben used for the extension and the house.

 

[HWBT_sometimes]

The SE drawings show what I am describing. SE is away this week which is a shame.

Inner wall is thermalites. Outer wall is concrete blocks. The house is bath stone with quoins.

The wall is a few courses high. Not the end of the world to remove blocks if needed.

I cant ask BC. Ive already been told they "don't design", hence why I am asking on here whilst waiting for SE to return. I dont mind asking BC if a "design" provided on here is OK. But thought there might be a standard way of doing it.

I think a wall starter and a corner block setup would work but as stated there wont be a 150mm cavity then.

Thanks

 

[stevie888]

I'm afraid I'm having difficulty in believing that any designer wants that detail.

BC will very soon tell you what is NOT acceptable. I think the l;east worst option now would be to extend the outer leaf to the left as drawn and use a Firfix to link it to the existing, but get BC agreement to whatever you do.

There is a remote chance that the planners might start to worry about side projections here by the way.

 

[jj4091]

As ivor Windybottom say, if the blocks were returned across the cavity and secured to the bathstone with another starter kit I would think that should satisfy your requirements. I'm not a builder though so as others are saying ask B.C. if they woul be happy with it. Why have you got a 6 inch cavity is this a new building regulation.

 

[Ivor Windybottom]

150mm is almost standard nowdays.

Hopefully a narrower part of the cavity would be tolerable. The original building already spans the cavity anyway. The overall insulation is the real goal, doors and windows have vastly lower insulation, we all accept that they're necessary and make the cavity wider to compensate. IMO making the cavity 2" wide over a brick length would be similar - a less well insulated part of the wall, which happens to be where it was already compromised anyway.

You probably need to assess the building as a whole, with a length of narrower cavity and ensure the thing as a whole complies. Hopefully the 150mm cavity was a little over-designed, so after making this corner a little less well insulated you'll still be OK.

Remember that the brick in this spot will be double-thickness, so this adds back some of the insulation you'll lose from that narrower cavity.

 

[HWBT_sometimes]

Thanks for the suggestions.

I have asked the building inspector if this would be ok.

 

[Ivor Windybottom]

I'd make it a full brick length inside the cavity, to resist it cracking if some differential movement does occur.

 

[jj4091]

150mm is almost standard nowdays.

Is that evenwhen using thermalite on the inner skin.

 

[jj4091]

Thanks for the suggestions.

I have asked the building inspector if this would be ok.

Yes that is what I was suggesting except that when the blocks are returned across the cavity it will be completely closed not partially as in your drawing

 

[Ivor Windybottom]

There's no reason to do anything with the inner leaf, it butts into the wall as normal.

Only the outer needs the extra return, so that it contacts the adjoining wall.

 

[HWBT_sometimes]

Building Inspector prefers the first option of the 200mm corner. So of the 150mm cavity, 100mm block.

He also said I would need to "insure i have damp and thermal protection in place". I'm guessing that's a 100mm strip of 50mm insulation CW4050 (or a cut in half CW4100 as being used) to fully fill the cavity in that small section.

where would the DPC go? to the outside of the new wall starter on the house wall?

Thanks