Timber Framed Extension - construction method?

[iam.tradesman]

Good evening and Happy New Year to all....

I wonder if there is anyone here who could give me some help/advice regarding the construction of a rear single store extension which i will be starting on my own house in a few months (when there is less chance of frost)

Due to size of extension i don't need planning permission, and have already paid for building control to oversee the work.

I want to construct the extension with an timber frame inner skin and brick outer skin. With a timber suspended floor in the middle of it all. I figured i will save money this way as i can do the joinery work myself and will save money on materials and labour over the Brick, Block & Slab method.

My first question is:

What kind of construction preparation is needed before the timber frame and floor and be installed?

I was thinking of digging to clay and pouring concrete foundations and coming up with a few courses of brick & block and running floor joists between/on top of the block (above the DPC) And sitting the timber frame on top of the inner skin of the block.

Is this the way is supposed to be done?

Any help/advice appreciated.
Regards

 

[^woody^]

Yeah, the foundations are the same as for a normal masonry extension, 1m down, 600 wide concrete, cavity or solid wall the thickness of the superstructure wall.

You'll need an oversite slab or geo membrane and gravel below the floor void, and probably best to have the floor joists on hangers.

 

[iam.tradesman]

Thanks Woody.

How much of a gap between the gravel and the floor joists would be acceptable?

Does the timber frame need to have OSB on the outside? Or can the breather membrane just go straight over the stud and insulation?

Is the idea that any condensation which forms on the Breather Membrane should run down into the cavity and out through weep holes of the outer skin?

ps... i have lots of questions.

 

[^woody^]

There is a minimum of 100mm subfloor void
IIRC, but check that it might be greater or less but there is a minimum dimension.

A timber frame needs a sheathing sheet to provide racking resistance (twisting or folding of the frame). It does not need to be OSB.

There needs to be a drained and ventilated cavity. The detailing of this at the top, bottom and cills and heads of openings is crucual. It's not just about weepholes.