Extending timber frame house over garage query

[roach]

Hi folks,

We've been living in this house for 4 years from new. It's one of those new fangled timber frame jobbies which I'm assuming is single skin brickwork outside of a timber frame with some sort of vapour barrier and insulation between the brickwork and drylined board inside. Part of the house is single storey on the side of the house which contains a garage and breakfast area off the kitchen as can be seen below.

Untitled

• roach
• 4 Feb 2010
• 1

What we intend to achieve eventually is to convert a 1/3 of the garage into a utility room and the other 2/3 into a toy/games room and then extend above the garage to give us another bedroom with en-suite.

I want to crack on with the garage conversion myself quite soon and get the shell of the extension done by a builder in a couple of years.

Say I complete the garage conversion, would the subsequent work on the extension above affect the work done or would they need to disturb the downstairs outer wall to strengthen it for the extra weight?

I think that the foundations would be suitable for the extension as somebody has done something similar in the same road as ours and I don't think they did anything with their founds, and the slab would most prob be the same all round right?

Any other considerations/possible problems I should be thinking about?

Thanks
Tony

 

[noseall]

You are likely to need to expose the foundations to prove suitability for the extra load. This can be done externally.

"because our neighbours did" is unlikely satisfy building control.

However you are also likely to have to step the second story extension back from the existing property line to satisfy planners. This will involve steel at first floor joist height and may affect foundation suitability.

If you do end up having to use steel and subsequently a structural engineer, then let him have a squint at the (suitability of) foundations.

If B.C. are satisfied with foundations and your proposals then fill yer boots.

 

[roach]

Thanks for the info.

Exposing the foundations shouldn't be a problem.

I'm hoping that I won't have to step the extension back because there is another 4 bedroom design house on our estate that is pretty much exactly the shape ours will be after the extension. Ours is the three bed version of the four bed without the extra bedroom on top of the garage.

Yes, I see what you mean about the steel. Could that possibly mean strengthening the single skin walls to support the steel perhaps by having extra pillars?

Edited to add: Is this how a builder would approach it:

1) Take the roof off the existing first floor
2) Put the lintel/steel in place
3) Brick up the external walls
4) Put the roof back on
5) Put the windows in
6) Clad the walls inside with insulation/ Vapour barrier and plasterboard

Obviously this is very simplified, but this looks like the opposite way of building a timber frame structure right? Normally the frame would go up first?

 

[roach]

I realise now that I'm going to have to have an RSJ spanning what is now the garage roof to support the front wall of the new extension. What I'm puzzled about though is how it will be supported on the exterior wall as this is single leaf brick. Am I right in thinking I cannot use this wall to support the RSJ as water will track in and and damp?

 

[noseall]

I realise now that I'm going to have to have an RSJ spanning what is now the garage roof to support the front wall of the new extension. What I'm puzzled about though is how it will be supported on the exterior wall as this is single leaf brick. Am I right in thinking I cannot use this wall to support the RSJ as water will track in and and damp?

You would normally add an internal skin of masonry to the garage if it does not have one, thus allowing you to carry on the internal wall up to the second floor.

However as yours is timber frame, then i guess you need to form the internal walls from timber. As this new internal wall will be carrying the first floor loads, then these walls will still need to sit upon foundations.