Single Storey Extension - 1900's - 1920's home.

[liam1369]

Good Morning Everyone,

I am asking for some advice for a project I am about to embark on for a friend who is trying to extend his existing home at ground floor level only. The extension will occur at an existing profiled windowed wall and the existing cavity wall at ground floor will be removed to allow for the extension.

However, owing to the profile of the wall, as well as it potentially being load bearing with the joists (see attached) I am initially thinking he will need some steelwork transfer beams with plates above to pick up this perimeter cavity wall. This creates an awkward steel beam arrangements with angled connections.

Has anyone had similar difficulties with a project like this? Or can provide better advice in terms of methods to allow for this extension? I have attached a pdf which includes some annotated photos and plans.

The new extension will also require new concrete foundations, however, I believe owing to this house being constructed in the 1900's to 1920's, I believe it still may have brick foundations, can anyone comment on any potential underpinning issues or considerations that are typical for extensions.

Any advice is hugely appreciated and if you have any questions or clarifications I am keen to inform.

Regards,

Liam

 

[liam1369]

 

[LittleInch]

Well I got away with the bottom of the underpinning being 1m below ground, but the ground beneath was virtually commercial grade sand and gravel so the builder persuaded the building inspector he didn't need to dig any more. Good old London clay might need to be deeper.

Underpinning is a little different to new foundations.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[liam1369]

Hi Littleinch,

Yeah it is case per case, maybe a reinforced strip is more suitable for the one you mentioned.

This current one I have is London clay, so I will be specifying 450 below and then 1m deep. So excavation will be at least 1.45 - 1.50m deep.

 

[liam1369]

Hi Enable,

I am considering using a portal frame to take the beam down as per your proposal.

A lot of literature recommends the use of a steel box frame but I am not sure what the bottom steel beam of the box beam is doing, is this simply there to increase the bearing onto a ground beam slightly? Can't really see the benefit of using a box frame as opposed to a steel portal frame with pad foundations.

Liam

 

[kostast88]

It is there to distribute the load - instead of applying a point load onto the existing foundation. It helps with bearing. Its is very common with frames on top of existing foundations (small residential jobs).

 

[Enable]

I'm going with Britain is just a weird place to build. See here:

https://betadc.co.uk/box-frame-or-goal-posts/

As you suggest, seems like people are using the bottom member for bearing to avoid additional footings underneath posts. If the frame is coincident with the edge of the exterior wall, this might work and is what seems to be the case in the above document. The idea being to cut the exterior wall to elevation, level the wall with a minor amount of concrete/cement, and place the new lower chord of the frame on top (presumably bolted in the flanges). Allegedly this is a cheaper alternative in Britain, if viable.

This would not be cheaper in Canada. I can drop a guy off in the morning to dig a hole while I pickup a truck load of concrete bags from Home Depot, make a pit stop at Tim Hortons for a sandwich (bring one back for my guy as well...I'm not an arse), and have my footings done in an afternoon. So odd to see people go through hoops to avoid this. They are designing additional moment connections between the beams to avoid footings for freaks sakes!

On an unrelated note: I sometimes teach a course on restoration of existing buildings at a local college, and I always like to include interesting little projects into the mix to give students the opportunity to really think about the practicalities of the trade. I like this project because of all the seemingly small considerations that add up to quite a bit (temp shoring, existing façade, water management, temp hoarding during construction, etc). If you would be okay with it would I be able to reproduce some of our discussion / your pictures in my lecture notes/handouts? If that'd be alright I would like to give credit where it is due! This forum doesn't like us posting our email, but I am easy to find (for you to email me your details name/company). Just google my username and add contracting to the end. My email is what you'll find for the generic information email, found at bottom of the homepage, but instead of information, use "allan" at the rest.

 

[liam1369]

Hi Enable,

Of course, it will be a pleasure.

Liam