New timber frame extension

[pudding]

Hi all,

 

So I'm finally getting around to starting to properly plan a new extension and have a friend who runs a oak/timber framing building company coming over later this week to chat.

 

So our current house is like this, with the extension to the bottom right, SE:-

 

 

 

 

 

And here is my current plan and pics using Live Home 3D.

 

 

 

 

Current ideas and plans for the extension are to use an insulated raft foundation (Kore? had a quick look and downloaded their brochures )if possible for the best insulation and should hopefully be relatively quick and easy. I'm hoping this wouldn't be an issue partnered to the current house which has normal strip foundation, or the old stone barn on the left of the pics has nothing.

 

It will have a flat green roof with 2 large triple glazed flat rooflights. All glazing will be triple glazed and have a large bi-fold in the larger room.

 

We'd ideally like an internal structural timber frame on show, and then externally will be cedar clad to match the newer part of the current house. Would oak be sensible for the internal structural frame? I have concerns about the timber drying out and warping and cracks between the old house and new extension.

 

There's not much external wall, but I'm proposing to have this as a timber frame with either PIR or EPS outside, then full fill with 100 or 140mm frametherm and perhaps internally insulated p/b, to try and target u<=0.15. Roof I'd like u<=0.12. Both of these would be better than the current house.

 

Access to the new extension is through the kitchen sliding door. New rooms will be a larger dining room, and the smaller a study/spare bedroom.

 

Any comments welcome

 

Edited September 24, 2019 by pudding

[pudding]

So a new slightly revised design is like this:-

 

 

Met with a friend who has a structural timber framing & building company. Current plan is to carry the work out under a building notice. He's given me the contact details of a structural engineer friend who I'm meeting next week to talk about getting the designs/calcs done for the timber frame and slab etc. In prep for this I've come up with the following for an initial floor/wall design. Lots more little detail sketches to come for existing wall/roof junction, existing roof/new flat roof junction,  roof skylight detail and also oak timber frame/new timber wall as below junctions.

 

 

It's not the passive slab I've mentioned in the previous post but should give pretty good performance. Any questions or tips massively appreciated.

Edited October 1, 2019 by pudding

[pudding]

Realised I missed of the 12 or 18mm OSB sheet on the outside of the timber frame before the 130mm PIR in the above sketch. Does everything else look good apart from that omission? I've not put on there a VCL which could go between the p/b and timber frame if needed?

Edited October 2, 2019 by pudding

[Carrerahill]

23 hours ago, pudding said:

Current plan is to carry the work out under a building notice. He's given me the contact details of a structural engineer friend who I'm meeting next week to talk about getting the designs/calcs done for the timber frame and slab etc. 

 

It sounds like you are planning on doing this all properly, I would just get the BC drawings done and do it without dubiety from the beginning - building notice sounds like a good plan, but anyone who I know who has tried to use it has ended up with it back firing. I also suspect on this case they will ask for drawings anyway - unless doing it through notice lets you break ground sooner I would advise not too.

 

Would I be correct in suggesting that your friend suggested going this way? Often those tasked with getting it planned up and approved do suggest things like this as it let's them hopefully bash on ahead rather than just sit down, and get it drawn up. 

[Carrerahill]

17 minutes ago, pudding said:

Does everything else look good apart from that omission? I've not put on there a VCL which could go between the p/b and timber frame if needed?

You could spec foil-baked PB and that kills two birds. 

[pudding]

Thanks for the reply. Yes my friend who runs the building company suggested the build notice route as he doesn't think there's anything too complicated about it. There's no rush and plenty of time to get drawings done if needed. We're not planning on starting until next April. I guess as long as we make sure BC are happy with anything we do beforehand, and I'll be sending them sketches of various details if required, hopefully any unexpected costs can be avoided.

 

Foil back p/b would be a nice easy solution. Any issue with the board joints though? Or would it be enough to have them meet on the studs and then the joints will be deemed vapour proof enough?