Help with extension costing/viability

[TheRivieraKid]

Hi all,

 

I'm after some advice from the experienced folks here. I don't want to spend money unnecessarily on architect etc. as we're in the early stages of buying a renovation project house in the South East.

 

It's currently a three bed chalet that we'd be looking to extend back, double storey, 8m wide x 3m deep to stay within PD. This would create a larger kitchen and utility room, separate playroom and an additional bedroom + en suite upstairs. The build would be a rendered finish so I assume block work instead of brick.

 

all in 48sqm on a 24sqm footprint. Pitched roof and concrete tiles to match existing etc. I want to know if it's actually possible for this to come in at £2000/sqm (not including kitchen and bathroom) or is it totally unrealistic? We have an extra £100k on top of the purchase costs but that's really it. The plan would be to leave the en suite room empty to fit a year or so down the line, and the kitchen can be financed separately.

 

I understand I'm asking how long a piece of string is, but I'd rather know the feasibility now before we get any further in the purchase process. Lastly, I'm quite handy at DIY stuff, and wondering what kind of labour I can put in myself to bring the overall costs down?

 

Thanks

[Olf]

11 hours ago, TheRivieraKid said:

I'm quite handy at DIY stuff, and wondering what kind of labour I can put in myself to bring the overall costs down

After my extension experience:

- excavations for foundations: you can try yourself on hired digger, I was happy to leave it to the builders because of site layout and ground conditions

- foundations: I used premix so with 30min pour the time was of the essence, I left it again to professionals to get the level straight. 

- blockwork: something that can be done by a DIYer

- joists: definitely DIY

- roof: considering it is pitched and must merge with the existing building, working at height and slope I'd leave it to a roofer 

- internal finish - all yours

 

To the main question: try to figure out ground conditions (there may always be surprises, but you will get an idea) for foundation cost, check for drainage location and levels as you need to connect the kitchen and ensuite, and there might be some drain close to the building requiring moving/building over. These 2 factors added a lot extra to what I hoped for.

From the ground level on you can get accurate figures, with 2nd storey costing you next to nothing in the grand scheme of things, as foundations and the roof would have to be done anyway regardless of the height.

 

 

 

[TheRivieraKid]

Thanks for the info, that’s really helpful. I told my wife I could probably dig out the foundations to save some money. I think she got a bit scared at that point!

Do you think it’s worth getting an architect to come and have a look at the site to get a better idea of local costings, or do you think that’s just wasting money? I’m really worried that it may end up costing more than we can afford, so would rather know before we exchange contracts.

[JohnMo]

Two factors come mind with cost, are paying someone to do it or doing quite s bit yourself?

 

Have you thought about Durisol blocks, very DIY, quick, you can render directly to it.

 

£2000/m2 is realistic, if you purchase wisely, that could include kitchen and bathroom.

[Olf]

5 hours ago, TheRivieraKid said:

Do you think it’s worth getting an architect to come and have a look at the site to get a better idea of local costings

Hell no! You seem to know what you want, so you can make the sketches yourself. If your builders will be anything close to what I experienced, they will ignore the drawings anyway, verbal communication with multiple repeats being the only way (which highlights the bonus of DIY - you know exactly what you want and how).

You will need a structural engineer though, for the foundations at minimum. He/she should be able to give you necessary information. You can inquire local folks now, they should have good idea of local ground conditions - few hundred spent at this stage may save thousands potentially wasted later. Some also can provide drawings for BC or direct to a technician doing that  - of course that is the area you can DIY and with good SE taking control of the details, you save money upfront and time (and money) later. I was glad not to have architect in the loop on occasions where quick decisions were required, but honestly could not cope without SE.

And triple check the drainage - location of ours wasn't obvious, and when found it (bang on in the middle of planned extension) it was a nasty shallow, low slope pipe. Low slope meant diverting was not possible, shallow meant complicated and limiting foundations/floor structure.

[TheRivieraKid]

Never heard of Durisol blocks. Looks interesting. I wonder what the long term integrity of those would be. Definitely one to consider.

 

Thanks, Olf. There is actually a manhole cover around 2m away from the back wall in the middle of the potential extension. We have local searches raised, so I assume this will detail whether that is a public sewer line or not?

 

Edit: I actually have a set of drawings from one of the neighbouring houses that had a similar extension a few years ago. I guess I can just show this to builders to get a rough idea.

Edited December 10, 2021 by TheRivieraKid

[JohnMo]

Look up the history of Durisol, they are the first ICF block, been around since the 1940s.  There's a good photo on the internet, where a hurricane hit and the only building standing was a Durisol build house.

[Dave Jones]

48m x £1500 for cheap = £72k

 

more realistic using trades 48m x £2000 = £96k

[Olf]

On 10/12/2021 at 21:01, TheRivieraKid said:

We have local searches raised, so I assume this will detail whether that is a public sewer line or not?

Nope.

'Sewers which were private before 2011 but are shared with more than one property, have now become the responsibility of the sewerage
company for maintenance – and these may not be revealed on the maps provided with the search' was the extact wording form my searches.

Translated from legalese: They have no idea what is in the gardens .