Advice on size of extension and floor space

hoopsbhoy

Hi,
Quick question on size of extension in terms of floor space.
I agreed with the builder that the extension was to be 11ft (L) x 14ft (W) in size. My requirement was for 11ft x 14ft of floor space and this was my interpretation of what was agreed. 154 square foot extension.
However, the builder has today poured the foundations and the outer edge of the foundation is 11ft 2in from the existing back wall. I'm assuming that the 9" cavity block will go in the middle of the foundations leaving the outside of the block approx 10'9" from the existing back wall and with the width of the block, insulation and plasterboard I'm estimating that my floorspace will only be about 9'9" x 13'6".
Have I misinterpreted this or misrepresented what I wanted or has the builder made a mistake? What would be the usual interpretation of the size of an extension?
If you ask for a 150sq ft extension should you get this amount of floor space or is this usually regarded as the size of the exterior of the extension?

Any advice appreciated.

Thanks

Poor Uncle Tom

Asking for 154 sq ft of an extension, would be for 154 sq ft internal area in my books. Without drawings or a specification or a contract it is going to be tough and saying someone on the internet agrees with you isn't going to help.

You are the one going to have to pay for the extension and the one going to use it. Don't continue with anything you are not happy with and make the builder aware of this as soon as possible.

hoopsbhoy

Poor Uncle Tom wrote: »

Asking for 154 sq ft of an extension, would be for 154 sq ft internal area in my books. Without drawings or a specification or a contract it is going to be tough and saying someone on the internet agrees with you isn't going to help.

You are the one going to have to pay for the extension and the one going to use it. Don't continue with anything you are not happy with and make the builder aware of this as soon as possible.

Thanks for that, we have a basic contract drawn up which states a 154sq ft extension but it is obviously not specific enough and open to interpretation. Bit annoyed at myself for not making sure everything was specified in writing, hindsight is great!

I'd value any other opinions from anybody in the building trade or anyone who has had an extension built etc
Thanks

BryanF

Employ an arch or arch tech to visit the site tomorrow/ Monday and meet the builder, you can outline your concerns and have someone on your side that knows the general accepted practice.
Ps 9" blocks are no longer exceptable and drylining is a poor option in a new extension.
One thing that we may not have considered is the builder intends to place 215mm block ( block on flat) and install external wall insulation outside the block? Again, get some independent consultation at your meeting. And next time have it from the start

hoopsbhoy

BryanF wrote: »

Employ an arch or arch tech to visit the site tomorrow/ Monday and meet the builder, you can outline your concerns and have someone on your side that knows the general accepted practice.
Ps 9" blocks are no longer exceptable and drylining is a poor option in a new extension.
One thing that we may not have considered is the builder intends to place 215mm block ( block on flat) and install external wall insulation outside the block? Again, get some independent consultation at your meeting. And next time have it from the start

Thanks Bryan, I wasnt aware there was any issue with using 9" blocks, that it definitely what is stated in the contract....?

I have spoken to several people about the standard practice and everyone I have spoken to incl architects and another builder all said the standard is internal floor space.

In any case I have since spoken to the builder who is adamant that the standard in terms of size is exterior dimensions so we're both coming from different angles on what is "standard" and unfortunately for me I didnt have it specified in the contract. At this stage I'm obviously disappointed but have decided to just leave it as is and asked the builder to insulate externally (internal insulation is what had been agreed in the contract) as a compromise.
It wasnt really worth trying to change it now with foundations already poured and it is further complicated by the fact that the foul line / sewage pipe is approx 11'3" from the existing back wall and would have had to have been moved in order to go out the intended length, added to the complications of getting a mini-digger in/out (again) to the back garden of a mid-terrace house with no side entrance!

Thanks again for your replies.

bryaj

Floor areas are measured internally.

You have instructed the builder to insulate exterrnally - are you aware of cost implications/additional costs involved?

martinn123

Lots of differing interpritations, so from one who does an extention or two, can I say the addition of '' external dimensions'' to the wording of any quote, or contract would have helped here. Hindsight.

However I read the expectation was for 11' internal with the sewer line only 11'3'' from the house.

How could anyone interprit this other than external measurement, otherwise the foundations would be over the sewer line.

sydthebeat

BryanF wrote: »

Employ an arch or arch tech to visit the site tomorrow/ Monday and meet the builder, you can outline your concerns and have someone on your side that knows the general accepted practice.
Ps 9" blocks are no longer exceptable and drylining is a poor option in a new extension.
One thing that we may not have considered is the builder intends to place 215mm block ( block on flat) and install external wall insulation outside the block? Again, get some independent consultation at your meeting. And next time have it from the start

im sorry, but i have to pick you up on this.

Cavity block construction is STILL an acceptable method of construction as per the building regulations, even if it is probably the worst type.

There are acceptable details as to how it should be constructed.

BryanF

Sure, but why would you use them?

hoopsbhoy

martinn123 wrote: »

Lots of differing interpritations, so from one who does an extention or two, can I say the addition of '' external dimensions'' to the wording of any quote, or contract would have helped here. Hindsight.

However I read the expectation was for 11' internal with the sewer line only 11'3'' from the house.

How could anyone interprit this other than external measurement, otherwise the foundations would be over the sewer line.

We only discovered that the sewer line was at 11'3" when the foundations were being dug, we knew it was out there somewhere not far from this point but only discovered the exact location after digging, well after size of 11ft (internal in my opinion) was agreed

hoopsbhoy

bryaj wrote: »

Floor areas are measured internally.

You have instructed the builder to insulate exterrnally - are you aware of cost implications/additional costs involved?

thanks for that - yes I understand external insulation is more expensive but have agreed with the builder that he will absorb the additional cost due to the 'misundertanding ' or 'miscommunication'

scwazrh

hoopsbhoy wrote: »

thanks for that - yes I understand external insulation is more expensive but have agreed with the builder that he will absorb the additional cost due to the 'misundertanding ' or 'miscommunication'

I would get that in writing as it is a fairly substantial extra cost to externally insulate as opposed to internally.
Also be aware that if there is any extension walls that line up with existing house walls , the new block work will have to be stepped back to allow for insulation and as such would be off centre on the foundations that are already poured.