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We moved into a new-to-us 100yr old house a few months ago. Ideal plan was to get a full width single storey extension across the back - but a couple of builders have come back with quotes and OMFG the cost!! 😳😳
Soooo - now we're thinking a 8ft x 8ft ish utility will do the job just fine! 🙂
The main sticking point is the ground at back of the house is raised (this is where the original outhouse/coalstore would have been). And a big cost of the full extension was digging all this out to get proper footings in. Could a much smaller single storey building be built off a slab of concrete instead? I presume conservatories don't need full footings if we had to go down that route?
Pic of area below - it's a mess I know, but it's probably been there for the 100 years the house has. And one of the reasons we bought the house is because it has scope for improvement...
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What about a timber frame extension? Do they require smaller foundations? IANAB
Digging the footings is something you can just DIY - hire a few skips, spend a few WEs shovelling dirt etc - it's tedious but very simple. I did the footings for our workshop - all dug by hand, filled 4 large skips. Building control came and inspected the hole before we poured concrete in it. Had the foundations finished and signed off before the brickie turned up to start.
before the brickie turned up to start
Was your brickie any good?
Strip footings need to be a minimum of 450mm below ground level (to the top of them) to avoid frost damage, how deep they go from there depends on the ground conditions/where your existing ones are. A raft slab is a viable alternative, have a look at the top post here for typical sections around the perimeter and existing which would need to be modified slightly for you depending where your floor level is/existing foundations are.
A conservatory still needs a proper foundation similar to a house, possibly only 450mm wide concrete strip instead of 600mm or wider but it still needs one.
Get a mini digger and clear the site yourself. Cheaper and more fun.
Where's that soil pipe drain to?
Digging the footings is something you can just DIY – hire a few skips, spend a few WEs shovelling dirt etc – it’s tedious but very simple.
We'd have to go down to ground level (as on left of pic), and then down again for footings - and I'm 54 and don't have the energy for that sort of thing anymore! 20 years ago yes. 🙂
We used to have quite a big old house, built in 1838. The front half was built on top of a much older cellar, so had foundations about 2 metres deep. The back had foundations just 1 brick deep. I found out when the concrete floor in a back room cracked. It was only about 20mm in that corner - straight onto dirt and when tidying it up I exposed the bottom brick and was able to poke my hand through and came into fresh air outside.
The house used to "breathe" quite a bit from summer to winter with cracks opening and closing with the seasons. Nothing to worry about though - gravity was holding it up.
Was your brickie any good?
A very interesting question 😉
Get a mini digger and clear the site yourself. Cheaper and more fun.
We hired one and had to take down a neighbour's fence to get it round the back of the house. Turned out none of use were skilled enough to use it efficiently and we basically had dug the footings by hand before anyone mastered using the thing. I quite like tedious hard work, like digging holes or shifting tons of sand from A to B, quite therapeutic - just totally switch off and get into a groove for hours.
you will likely need to found anything in the natural ground. the actual digging is the cheap bit.
the expensive bit is getting rid of teh excavated material. 8m cube a go (give or take) and the material bulks up by 1/3 when you dig it. do some measurements and some basic maths to see how much you will need to shift. then phone some grab lorry companies - I`d budget maybe £300/load. you might get cheaper for multiple trips. looking at the height of the raised area you might end up spending £5k before you even build anything.
- also material costs have gone up by about 50% since covid.
for any foundation advice you will need to speak with a structural engineer. you should probably do this before you speak to a builder.
a lightweight conservatory may be feasible off of the raised area.
Nothing to worry about though – gravity was holding it up
Fan-bloody-tastic!
Your foundation depth really has little to do with the weight of bearing, for housing anyway. The pressure on founds from a single storey and two storey really isn’t massively different. Depth is more about going down to undisturbed clay that’s firm enough to support and also not water bearing. If you have disturbed clay, or water in it, it can heave and shrink with seasonal conditions. Any movement like that can cause cracks or if it’s compressible cause structural failure.
You could use a raft foundation as an alternative but you’ll need an engineer to design and certify it.
Will probably depend on ground conditions etc.
Next door neighbours binned of having their extension done due to needing piles due to ground makeup.
Anything substantial will probably need a ground investigation and structural engineer input.
Have you had your quotes done for the smaller option ? Is 8x8 really worth doing when clearly you want more than that ?
Are you sure the OMG price isn’t just because how things are at the minute ?
We had bathrooms done about 8 months back and the trades people said they were stopping quoting as costs were rising that fast.
ie they would give a price but they say the cost would 99% be higher as everything was going up daily !
Personally I would wait until you can either afford to do the extension you want/prices return to normal
We don't 'need' a full width extension it was an idea to add value (and been watching too much Love It or List It! - there's only two of us living in the house (19yr old daughter lives away 95% of the time).
The only thing we actually need is a barrier between the back door and the rest of the house. Somewhere to dump shoes, coats, put a tumble dryer and a holding area for the dog before he rampages around the house with wet muddy paws! 🙂
Truth is we inherited a sum of money when the wife's mum died. We were going to go full tilt down the full extension route, but then we both got Covid a few weeks ago and I was quite ill with it.
It made us re-think what we wanted and we decided we didn't want £50-£60k+ tied up in the house. We're both in our early 50s and we'd rather spend more on doing nice things and scale back on the house.
Before we go back to builders we'd just like some idea of what is feasible.
Anything substantial will probably need a ground investigation and structural engineer input.
Unless you know you're sat on clay you just dig the footing to the standard spec and call out Building Control who will take a look and say 'fine, you can pour now' or 'nope, dig a bit more and call me back at another 0.5m and we'll see what that looks like'.
We had a similar situation with 5ft of made ground (rubble fill with patio on top). We ended up digging a trench (~£600 for digger, labourer and skip), getting 5 tubular piles put in and a ground beam cast over the tops of the piles (£4k). The piles added probably £3.5k compared to if we were starting at natural ground level. I had worked out a slab would have been a bit more expensive, but there wasn't a huge amount in it. It's a lot of money for a tiny area, but it allowed us to open up a lot more internal space so worthwhile.
In your case could you go down a lean-to non-structural sort of structure, if it's just for washing machine, shoe store and dog bed?
In your case could you go down a lean-to non-structural sort of structure, if it’s just for washing machine, shoe store and dog bed?
@Mowgli - thanks - that's what we're steering towards now. And money in the bank not in concrete.
OP, where are you located?
the only exempt extensions are a conservatory or a porch, conservatory has to be substantially glazed (2/3 roof area, 1/2 wall area) and a porch has to be on house's main entrance
Just had footings dug, predominately clay. They had to go down to 1.4m.
And yes extension prices are OMFG prices at the moment. Seems much doubt that they will 'go back down' though
Derbyshire.
Conservartories seems to have those lightweight tiles now. Are they still classed as conservatories?
Seems much doubt that they will ‘go back down’ though
If they do it won't be anytime soon. Some builders I've spoken too have two year waiting lists. And the soonest anyone (decent) could do anything was late spring/early summer next year. While people will pay the prices then they'll stay high.
Couple of piles/pads on the outer corners and cantilever a steel frame into the main house. It’s what we did for a small extension where footings were awkward due to a shonky extension next door we didn’t want to undermine or spend a fortune shoring up.
Steel frame might cost a bit but it’ll reduce the amount of earth you’d have to move and dispose of.