Timber frame foundations

[jntabbycat]

Hi all,

 

Does anyone have any details/drawings or even a sketch of a typical foundation for a timber frame extension where it is to be clad rather than a brick outer leaf. Normally 100mm brick then cavity then timber frame (sitting on brickwork). With no outer brickwork do I just build up a single wall to dpc and increase insulation on the slab inside? I have googled it but nothing seems very clear and most buildings have brick outer. Likely using 100mm timber frame with insulation over and in between.

 

Chris

[Tony C]

If you image search on google "kingspan timber frame" , you will get some section images of Timber frame and cladding (are you cladding with timber? or metal sheet?).

I am building Timber frame + corrugated metal sheeting with an architect, but they have not done details drawings yet...

[jntabbycat]

41 minutes ago, Tony C said:

If you image search on google "kingspan timber frame" , you will get some section images of Timber frame and cladding (are you cladding with timber? or metal sheet?).

I am building Timber frame + corrugated metal sheeting with an architect, but they have not done details drawings yet...

 

 

Thanks, will check it out.

 

We are partially cladding with Zinc and partially with cedar....or possibly painted black timber. Only a small extension really but should look nice. Be interested to see what your architect comes up with. Love corrugated sheet!

[Tony C]

I can share the section drawing once I have it.

Here is the 3d render image from our architect.

 

[jntabbycat]

Looks good from that image. This is what we’d like to build, finally (assuming permission is granted). Just a small porch with a downstairs toilet.

 

 

[Carrerahill]

3 hours ago, jntabbycat said:

Hi all,

 

Does anyone have any details/drawings or even a sketch of a typical foundation for a timber frame extension where it is to be clad rather than a brick outer leaf. Normally 100mm brick then cavity then timber frame (sitting on brickwork). With no outer brickwork do I just build up a single wall to dpc and increase insulation on the slab inside? I have googled it but nothing seems very clear and most buildings have brick outer. Likely using 100mm timber frame with insulation over and in between.

 

Chris

How long is a piece of string? There is no such thing as a standard foundation detail, this really needs to be fit for purpose. However, assuming ground conditions are good, I would go for about a 400mm x 150mm found, you could get away with 300mm but I think the 400mm will give a nice footprint. I would also be tempted to build up above ground level to DPC in brick or poured concrete so your kit is not sitting in the ground.

 

As for foundation depth, it depends what you opt to do, if it was me I would go down to the same height as the house founds, and pour a 400 x 150mm found, I would then use trench block to get you most of the way out then build a wall up to DPC level in brick or block, then fit my treated sill plate and build kit onto that. You then don't need to worry about the based of the build getting wet. You could run external cladding down over the wall slightly so you cannot see the base brick. 

 

Don't be tempted to go trench fill next to the existing house unless the house is trench fill in which case do go trench fill!

 

Addendum: I know some people may say that the found I speced above is too big for the type of build going on top, but I am designing the foundation in isolation to anything else, I would want to know my foundation is going to support itself and withstand and movement without cracking, the fact that the build weight will be less than a conventional build is actually another factor in the larger foundation size, without the weight above it, the found could be more susceptible to ground movement and thus failure. 

Edited January 22, 2019 by Carrerahill
Additional info.

[jntabbycat]

Definitely building above ground with brick up to DPC. Possibly engineering brick with a dark mortar so it looks ok. I’m more concerned with what happens with regard to connection of timber frame to the brick in terms of insulation. Single brick up to dpc and then frame on top is fine but the brick will need insulation on the inside presumably as opposed to cavity wall.

 

Hope this makes sense.

 

The actual footing will prob be same as house. Ground is very solid about 750mm down so BC were happy on rear extension with just 750mm deep. Want to use timber frame on front to keep the walls as this as I can and gain space inside.

[jntabbycat]

I’ve drawn this. Think it’s ok based on what I can find online etc.

 

not included makeup of wall just the timber.

 

single skin wall on top of footing with baseplate fixed above dpc.

 

From the bottom. 150mm blinded rubble or type 1 compacted, 1200 dpm, 75mm rigid insulation, vapour control layer, 100mm concrete, 50mm screed. Insulation around edge of slab 50mm thick.

[jntabbycat]

Looking at this again and with what I drew above it looks like I’ll have a cold bridge through the bricks with only 2” insulation between the brick and the floor slab.

 

any way round this?

[jntabbycat]

On 22/01/2019 at 11:39, Tony C said:

I can share the section drawing once I have it.

Here is the 3d render image from our architect.

 

 

Any update to this? Finally got planning permission, in to building regs now. Be great if you did have a section drawing of the wall/floor connection etc.

[Mr Punter]

Well @jntabbycat I would be really interested to see the plans and sections for this when they have been worked up.  It looks like a fair bit of this will not be timber frame as per your detail but the door and window. The corner post will need to be structural.  Be good to show the external paving level, as on the SketchUp it looks level with where you have the sole plate.

[Russell griffiths]

@jntabbycat you need to look at separating your timber sole plate from the cold brick, this is the area that causes problems, you can look at a product called Marmox, it is a structural insulation, you also need to look at your section drawing and design how your cladding will fit to the outer timberframe. 

I think you will find you will need an outer plywood, osb, layer then a breather membrane then a counter batten then cladding. 

By working this out you can determine where your frame sits in relation to the courses below, you may find to come in line with building regs you need minimum 140mm frame then osb then batten then cladding so you wall ends up being closer to 210 thick. 

Draw this up with marmox blocks underneath and you will end up with a far better building than just a glorified shed.