Reasonable extra cost for deeper foundations?

[Tweedledee]

We are six weeks into the build of our 3.5m extension on our semi-detached in south London. (3.5m out x 8.7 m wide)

Building control spotted a weeping willow 21.5m from rear of extension and insisted that 1.4m specified foundations were not adequate and we needed 1.8m. (On checking NHBC numbers. or what I could find online, this looked excessive to me and it turned out they were using data from London Surveyors, not NHBC.)

The builder brought in an engineer to recommend a solution and we opted for pads and steels, thus not requiring the dig to 1.8m all round. The builder said this was similar cost to just digging down to 1.8m.

The builder would not answer the question about how much extra for deeper foundations, but the best I could get from him on being pressed was to agree that it would be "a couple of thousand".

The roof is about to go and, and we have had a valuation from him and he is now requesting £2875 + VAT extra. I could just about stomach that only now he is claiming (it wasn't on the document) that that includes a discount of unnamed amount for a 3400 litre soakway which was to be built but could not be built due to saturated clay soil.

In my very rough calculations a soakway of that size would surely cost £1000+ to build so really the extra foundations are costing us £3875 + VAT, which is a far departure from the "couple of thousand" suggested.

Am I being overcharged? How do I proceed to get him to lower this figure: is there any way?

I have never managed to get sight of the engineer's report, despite asking, and I have no idea how much it will cost. The cost is not included in the above.

Generally there have been no other problems with the builders: all seem polite enough and the build has gone well thus far.

The cost on my quotation for soakway PLUS concrete tiled sloping roof PLUS fit (not supply) 3 qty VELUX plus guttering is £3650 + VAT. I've just never managed to find out the value of the soakway itself as he wouldn't tell me.

Dave

 

[noseall]

We did a job where the drawing gave the standard generic 1m dig but the house footings were 1.5m down in clay. Not only that but there were previous drain excavations in the ground which meant that our new trenches were susceptible to collapse.

So, all the trenches had to be shuttered. I can't remember the size but it was across the whole rear end of a 4 bed detached and went out say 3.5m or so. All in all 20+ linear metres of trenches.

Overall extra cost was in the realms of 5k.

 

[jeds]

Who specified all this for you? First of all your designer should have taken any influencing trees into consideration. Even if trees were not an issue there is no way of knowing how deep a foundation will end up without digging to depth. For that reason you should always include a priced contingency for extra depth. Secondly, I always list soakaways seperately because they often do not get dug (due to the very reasons you encountered) and so you always need to know exactly what the cost is so you can easily omit if from the contract. All sounds a bit sloppy to me. Unfortunately some designers want to draw pretty pictures but fall short when it comes to the really useful work.

As for the extra costs. you are looking at extra machine hire, nearly 4cube of extra digging and handling, 4cube of extra disposal and 4 cube of extra concrete. plus there might be some shoring up. I can certainly see a few grand in there. The bit that confuses me is that I reckon a 3400 litre soakaway would probably cost more than £1000. Probably quite a bit more. So to me the issue is not so much the extra cost but how much you should be getting off for the soakaway? Also you will be paying for the engineer. Which you really should have employed direct. Otherwise you have no privity of contract.

 

[^woody^]

We don't know the specifics so its not really practical to say what costs are reasonable

But with any extras, it is important to know how they will be valued, and not just be a random figure.

A dayrate, or a cost plus percentage are two ways to value the work, and if the means of valuing work is not specified at the outset or in the contract, then you should ask for a cost breakdown.

And then use similar methods to deduct the value of any work not being done

 

[Tweedledee]

The drawing was done by our architect who specified the 1.4m foundation.

The engineer was brought in at suggestion of the builder but I understood the builder was acting as main contractor and sub-contracting. Instead it seems he wants me to pay the engineer direct. So I guess I've taken someone on who is unlikely to give me impartial advice about how much I should have paid for the extra work.

No machines were used: extra digging was done by hand. No shoring used that I saw, in fact that's the reason that the builder favoured not digging to 1.8m all round, not needing to shore up.

The extra digging I saw was mostly at the pads.... does that sound correct? Since I still don't have the drawings from the engineer I don't know exactly how much extra material was removed.

The £1000 is my lowest estimate of the cost of that soakaway: the builder refuses to tell me how much he allowed for the soakaway. All I know is that on the quote it is £3650 PLUS VAT for the soakaway PLUS roofing work. So presumably the soakaway probably represents more like £1500 of that?

 

[joe-90]

If you don't know what you are paying for then no-one can make you pay it.

Tell him you want a break-down before payment is made.

 

[Tweedledee]

Having said on the phone that he'd do a breakdown, he now says in an e-mail that he wants to meet for a chat about the rest of the works.

And I still don't know how much the soakaway was worth on the original quote as he won't tell me. As a result I still don't know exactly how much I am being charged for the additional works.

 

[Tweedledee]

After demanding a detailed breakdown of the costs for the foundations showing original items vs extra, instead he produced a very broad breakdown of costs across the project, so that I could not see how the figure of £2875 was arrived at.

As I said to him that I thought I was misled to believe that the extra work would cost £2000 total, he says he will charge me £1200 only, though that value is based on believing that the 3400L soakaway (not built) was worth only £1200. (That's the discount he applied for not building it.)

Assuming the soakaway was really worth £1800 (my estimate), really what I've paid is £1800 PLUS engineer's bill of £500 (now arrived), which is £2300.

Also, I will later be paying over the odds for my roofing work to the tune of £600 as the quote was roof PLUS soakaway at £3650 (supply and fit membrane and concrete tiles on a 8.5m x 3.5m extension, and install three customer supplied velux + flashings). (All less VAT).

I fully expect that the builder will try to add much more on extras to "recoup" his "loss". A small bit of extra work was done just on Friday using one of his lads for half a day to do some blockwork, and I wanted to know now what that'll cost me and he won't answer the question. I want values on extras as they happen.

Also, he wants to knock through to the main house BEFORE putting the roof on the extension. That sounds unusual, and I know we will have no house insurance if that happens.

Dave

 

[noseall]

Also, he wants to knock through to the main house BEFORE putting the roof on the extension. That sounds unusual, and I know we will have no house insurance if that happens.

It's not unusual to install the lintel of a knock through prior to building the roof as fitting it after the joists are in is very difficult or in some cases impossible.

We usually make a hole big enough for the beam or lintel plus some wiggling room then stuff cavity batts in any gaps after the beam/lintel has been fitted.