Building a Domestic Extension in Stages

[limerockconstruction]

Need more info before being able to offer info on price, but your sub floor makeup is likely to be something like

75 screed
125 insulation
100 concrete
150 stone

Doing it your way would mean you would have to either shutter the top 250 of foundations or get in to dig the oversight out afterwards, neither of which is normal - Also having the extra 9 inches below ground gives the Brickie more chance to get it perfectly level by damp-course depending on who is doing the foundations.

 

[CHarr]

I have received a quote of £2.8k to dig and concrete the footings (but that doesn't include the concrete or pump hire - another £1k) and do the underground drainage. That seemed on the high side, so I looked around, finding a local plant hire company, who also do groundworks and offer a grab hire service. They hire mini-diggers (but I can't operate one!), but they will also hire them with drivers.

I asked them what I needed and they have offered digger + dumper (both with drivers) a concrete breaker (there's a bit to break out) and 3 loads for the grab lift. They will deliver the plant without additional charge, and have quoted an 8-hour day at £845 + VAT all in, expecting to finish all the excavation in a day.

I'll have to put the underground drains together myself (or hire a drainlayer), but using plastic push-fit fittings there's only about £100 of materials + my own time. I also have to do the concreting, or get help, but this seems a VERY inexpensive way of getting my build underway.

I expect there's a catch (but the company will work overtime at an hourly rate pro rata the day rate if they overrun), but this project is looking more and more like a self-build every day.

 

[CHarr]

Need more info before being able to offer info on price, but your sub floor makeup is likely to be something like

75 screed
125 insulation
100 concrete
150 stone

Doing it your way would mean you would have to either shutter the top 250 of foundations or get in to dig the oversight out afterwards, neither of which is normal - Also having the extra 9 inches below ground gives the Brickie more chance to get it perfectly level by damp-course depending on who is doing the foundations.

Just out of interest, the designer's spec has the build up in the order:

Stone
Sand Blinding & DPM
Insulation
Concrete
Screed

I am going for concrete foundations 450mm below DPM, so should have plenty of wiggle-room.

 

[limerockconstruction]

I have received a quote of £2.8k to dig and concrete the footings (but that doesn't include the concrete or pump hire - another £1k) and do the underground drainage. That seemed on the high side, so I looked around, finding a local plant hire company, who also do groundworks and offer a grab hire service. They hire mini-diggers (but I can't operate one!), but they will also hire them with drivers.

I asked them what I needed and they have offered digger + dumper (both with drivers) a concrete breaker (there's a bit to break out) and 3 loads for the grab lift. They will deliver the plant without additional charge, and have quoted an 8-hour day at £845 + VAT all in, expecting to finish all the excavation in a day.

I'll have to put the underground drains together myself (or hire a drainlayer), but using plastic push-fit fittings there's only about £100 of materials + my own time. I also have to do the concreting, or get help, but this seems a VERY inexpensive way of getting my build underway.

I expect there's a catch (but the company will work overtime at an hourly rate pro rata the day rate if they overrun), but this project is looking more and more like a self-build every day.

You have to look at it like this....

£845+ VAT is £125p/h - if they over run, your budget is going to alter dramatically - at least you know where you stand with your £2.8k fixed price

As for doing all the drainage etc yourself, I think you will find it a bit of a challenge unless you've not done it before (judging by another post you've not).

DIY = saving money, however, getting groundowrks done by a professional, it should be cock on!

 

[CHarr]

£845+ VAT is £125p/h - if they over run, your budget is going to alter dramatically - at least you know where you stand with your £2.8k fixed price

As for doing all the drainage etc yourself, I think you will find it a bit of a challenge unless you've not done it before (judging by another post you've not).

DIY = saving money, however, getting groundowrks done by a professional, it should be cock on!

There will be an additional cost if the job overruns, but a big proportion of the cost is the use of a grab lift to take away the excavated material (3 x 14t loads), together with the hire cost of a concrete breaker, which we will probably only want for the first hour or so. The only reason we will incur additional costs there will be if BC require deeper excavations, and my fixed price quote was also conditional on not digging more than 1m at that price (which was fair enough). The hire of the digger & dumper with operators actually works out at a very reasonable £54/hr, and if we overrun by an hour or two, I'm not going to be worried.

The drainage IS a challenge, but I've done plenty of general plumbing over the years, and although some will laugh, Wickes publish a very helpful 'Good Idea' leaflet (#74), there's a good interactive diagram of a typical layout on their website, and my local store has everything I need sitting on a shelf where I can browse and examine and ponder to my heart's content. I'll ask the building inspector to confirm that the intended layout is OK, when he inspects the excavation even before concreting. He was very helpful on his initial visit, and I wont even dig the trenches until I know he'll be happy.

My decision to self-build is based on cost saving, rather than on my own extensive knowledge of the building trade, but I'll be bringing in a full range of trades throughout the build. I also have a Chartered Building Surveyor with many years of practical experience on hand as a project manager, whose hourly rate is very reasonable, but I'll do some of the straightforward work myself. A tradesman cannot add value to some simple tasks, and I have plenty of time, being semi-retired, and don't have to do anything in a hurry.

 

[CHarr]

Things are going well: the excavations did overrun, but the total came in well under the alternate fixed-price quotation. I could have done without the electricity supply cable getting accidentally severed, but it was buried at a stupid depth, and completely unprotected.

Building Control said 'lovely job, carry on', so 12m3 of concrete went in this morning, and I have brickies starting on Monday to set out the walls and get in the brick/blockwork up to DPC.

 

[CHarr]

The walls are up, and the joiner starts work next week. I'm now looking for a roofer, and hope to be watertight in three weeks. The glazing company are measuring for doors & windows today, so we'll be secure, soon, too.

I just need to sort out the floor! I'm nearly ready to backfill over the drains and put in the stone sub-base before insulation & concrete. I've accumulated quite a lot of building waste (bits of broken bricks and cut blocks, mainly). If I break it up further, is there any reason not to use that material to form the first layer of my sub-floor (seems daft to hire a skip to take it away, only to have similar delivered in bulk bags)?

Does anyone have an opinion about the relative merits of traditional screed compared with liquid screeds?

 

[noseall]

How come you haven't done the floor yet?

 

[CHarr]

How come you haven't done the floor yet?

The drains run directly across the back of the whole house/extension right next to the foundations, so rather than excavate for both, and then have to shutter off one side, we decided to do the drains after the foundations. We have deferred the job until after the walls have gone up rather than have unstable ground at the base of the walls making working off trestles hazardous.

I put some cheap OSB against the insides of the trenches before mass-filling, so we have 'lovely' smooth sides to dig against. Max depth is 750mm, so there's no danger of undermining, and by next week, when the roof starts go up, I can be carrying on with backfilling, stoning, concrete and insulating in the dry!

Any view about DIY hardcore?

 

[noseall]

How are you going to lap the DPM?

Hardcore sounds ok. Big lumps at the bottom and give 'em a smack if they are a bit wobbly.

 

[CHarr]

How are you going to lap the DPM?

Hardcore sounds ok. Big lumps at the bottom and give 'em a smack if they are a bit wobbly.

The brickies lapped in 600mm of the DPM material all around before building up the blockwork off the DPC. It's currently neatly rolled up and taped out of harms way with brown tape, and once the floor is fully prepped, I'll lay the rest of the DPM with a big overlap and then tape properly before putting in the floor slab.

BTW, a secondary reason not to do the floor first is that the side extension is on the site of a former garage, and its concrete floor slab is still in place. It isn't level, and it is lower than the new floor, but it doesn't require any additional prep (& BC is happy), so the area that actually needs flooring 'from scratch' is only about 25% of the total area. My brickies were glad of a smallish job to fill in between two bigger ones, and they were available at short notice, so it made perfect sense to change around the normal order of things.

 

[harlingtonstraker]

sounds like its going well, do you have any pictures of the various stages
that you can share please?

 

[noseall]

I still don't get why you did not do the drains and all the oversite prior to building the structure.

Surely once the foundation concrete was poured and set, you could then merrily dig away with an excavator and do the drains.

Everything gets back filled, you build up to DPC, you then stone everywhere inside and out, hey presto a nice site with a level stone surface to work on.

Can you still get a digger inside? Do any drains need to pass through the structure?

Your idea sounds completely bonkers to me.

 

[CHarr]

Your idea sounds completely bonkers to me.

Just unconventional: that's all. But no, there's no way to get a digger in now, and anyway, hiring one for the day would be a sledgehammer to crack a nut - there isn't that much to dig - and we've done it by hand. The drains pass through the foundations in four places, and each was shuttered before mass-filling, and then the gaps bridged with lintels. We have only had to dig between those points to complete the trenches. Even the company that machine-dug the foundations said that it would be cheaper to hand dig the drains (and offered me a groundworker at £80/day). It has taken two days, so the DIY effort has saved £160, and that's money that can be better spent elsewhere.

 

[CHarr]

The drains were approved by the Building Inspector this morning, so I'm backfilling tomorrow, then preparing the sub-base for the floor slab. I'm hoping to be ready for concrete by the end of the week, but I've got chippies starting on the cut roof construction on Wednesday, and don't want to be in their way.

So far had no trouble finding tradesmen for each stage, but no one is interested in the roofing job, yet. Are roofers in short supply?