Build over single skin converted garage

[tomcat_]

Hi all,

I have a single skin garage adjacent to our semi detached house that is a 2020 build. Foundations are the same as the main house. That garage has been converted in 2021 by having stud walls inside the single skin. The single block skin has block piers across and on top are resting box lintels in order for the roof to rest.

We have obtained planning permission to build on top of the garage and below is the expected design:

Our structure engineer informs us that the easiest way to build the top floor is to build an outside block skin in essence forming a cavity with the current outside skin building the 1st floor extension all the way up and the roof will be supported on the new cavity wall.

Is there a way the current box lintels can support a light 1st floor structure build with timber rather than blocks, as this way we only need to take the roof up, build up with timber on top of the boxlintels and current outside skin?

Thanks for your input

 

[freddiemercurystwin]

If you add an additional skin on the outside you'd need to go back to planning. You're supposed to think about how its going to be built before you go for planning. I'd be doubtful those lintels would cut it unless they were over specified in the first place but your SE would need to confirm, probably need replacing with some steel beams, build the timber inner skin off them. What are those box lintels doing anyway, are they original, why don't the trusses bear on the single skin?

 

[tomcat_]

Thanks for your reply. The box lintels are original, and have them all around the garage, looks to me like bridging between piers on the place that there is not the main cavity of the house.
My SE is not font of the idea of building timber frame on top, as he doesn't see how 6'' timber will rest and also concerned about wind load and stability. An idea would be to get another opinion from another SE.
In a different conversion in an old victorian, the l shaped loft was done on top of the outrigger with timber although there was a solid wall.

 

[freddiemercurystwin]

Well you've already seen the detail showing how it can be done in your other thread yes? So it is possible. Perhaps try another more progressive engineer.