The best way to build my extension

A_Novice · 13 Sep 2018

Hi guys,

Just a bit of advice needed. Have been on before so hopefully you aren't sick of me yet!

Am speaking to architects to do the building reg drawings for my extension over garage. So I know what they are talking about when they go on about cavity walls, pad foundations, steel beams etc could someone explain how the extension could be built and possibly the best way.

The 1st floor will be timber frame construction with either tile hanging or brick skin. Got plans for both.

The flank wall of the garage is a single skin of block work which may have suitable foundations to support the load above.

I'm trying to understand the approaches for building onto this taking into account the foundations may or may not be suitable

E.g. Architect A has said the timber frame can sit on top of the flank wall.

Architect b said ignore the wall and run steel beams front to back and build off of that.

How do I know what is the correct way?

I appreciate there are probably lots of ways of doing this but what are the most common?

Any help would be appreciated

^woody^ · 13 Sep 2018

There are generally no correct ways, just different ways.

A_Novice · 13 Sep 2018

^woody^ said:
There are generally no correct ways, just different ways.

Cheaper ways then?

For example if the flank wall has suitable foundations can it be built differently without the cost of steel?

wessex101 · 14 Sep 2018

You are just going to have to dig a couple of trial holes and expose the existing foundation to see whether or not it is suitable. Trying to design it based on guesswork and assumptions is just silly.

Once you know exactly what you have got the designer should be able to make an informed decision on the most appropriate construction for the first floor (but that assumes you have employed a good designer).

A_Novice · 14 Sep 2018

thanks. I'm really just trying to get a better understanding on how these types of extensions are constructed.

wessex101 · 14 Sep 2018

Building directly off the ground floor walls would be most common and cheapest (closely followed by demolishing the whole lot and starting from scratch). You would only go to the trouble of putting steels in if the existing structure was not strong enough to support the new extension.

A_Novice · 14 Sep 2018

Thanks. So if the walls are adequate how does it work if it is single skin? Would a new wall need to be built on the inside on the ground floor?

wessex101 · 14 Sep 2018

I thought you said the first floor was going to be timber frame or single half brick skin with tile hanging? If so it will just go directly up off the ground floor single skin wall.

If the first floor is going to be a cavity wall then you will need the steels to support the inner skin. But then you are possibly getting in to the realms of demolishing the garage and starting from scratch as a cheaper option.

A_Novice · 14 Sep 2018

The first floor is going to be timber frame with tile hanging or with a brick skin. (probably tile hanging as supposedly easier).

So does that mean the first first floor if tile hanging there is no cavity so can just build it off the single skin wall. (foundations being adequate) assuming I have understood your message correctly.

I'm trying to work out if the wall isn't adequate to build off is the project worth continuing with as the costs will start to rise significantly.

I have no idea how much extra costs steels or demolishing the garage would add to the project.

Notch7 · 14 Sep 2018

If the garage was built at the same time as the house, it may the same footing -which could well be sufficient.

digging a trial hole down the side of a wall will give you a good indication.

A_Novice · 14 Sep 2018

Notch7 said:
If the garage was built at the same time as the house, it may the same footing -which could well be sufficient.

digging a trial hole down the side of a wall will give you a good indication.

Unfortunately it was built after the house.

I'll put a pic of the plans I have on here later. They describe the foundations and you guys will understand them more than me.

I can't physically dig down the side as the garage is built next to my neighbours garage. The only option would be the front and back. Garden slabs in the back and a block pave drive in the front make it tougher.

^woody^ · 14 Sep 2018

When you instruct someone to do the design, you should not worry about the technicalities, but only worry about the things that matter.

If say, you want an extension with a bedroom and bathroom and want it to match the house, then that's it and you let the designer design it based on what you want. If costs are an issue then say that and get something designed to that cost. If you want to keep the garage as wide as it is then you say that. If you don't want to dig new foundations or knock stuff down, then you say that. If you dont want to be lifting any heavy steelwork, then say that.

To sum up you tell the designer what you want, what you don't want, and want a cost for building it within your budget. And let him/her do their job. If you don't explain your criteria and requirements then they just plod on and do what they think, which is not necessarily the same as what you want.

It may be that you can't have something or things must be done a certain way because options are not possible or cost prohibitive. Then you discuss this and compromise or alter the design.

Footsoldier888 · 15 Sep 2018

You could consider taking an alternate approach and talk to a builder who has done the same extension on another house close by.

You can go down the architect route and pay for a trial hole to be dug but then find you get high quotes because the builder is not comfortable building in the method the architect has specified. If you go with the builder who did a good job four doors up say, they can use their designer/drawer to do the plans to their preferred construction method, which hopefully would come in cheaper. However it is possible the design will be less interesting and considered than one an architect will produce.

If you are going out a bit further at the back it is vital to get a drain survey done as shifting drains might even require permission from your water company.

noseall · 15 Sep 2018

Notch7 said:
I.

digging a trial hole down the side of a ~~wall~~ foundation concrete will give you a good indication.

A_Novice · 15 Sep 2018

Thanks for the excellent posts.

Being such a big commitment I am trying to get my ducks lined up first.

Out of interest how much would it add to the project if the flank wall had naff foundations. e.g. steel piers. Is it a show stopping amount? (i know you can't be exact)

There is little point me checking the foundations early if it isn't going to stop me proceeding with the project.

Ultimately i think i just need to bite the bullet and get a designer in to do the building regs and then get some concrete quotes from builders.

Do the foundations get inspected before the building reg application or does it just happen on site when the work starts?

Thanks

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The best way to build my extension

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