Basement thoughts

[puntloos]

Figured I'd open a specific topic to narrow my thinking a bit. So. BASEMENTS!
 

Functions: which things in your house do you have, or would you loved to have had in a basement (if you only could)? Which things you have in a basement do you regret? For example:

- An electrics closet (servers? consumer unit?) might be 'tucked away' nicely but I can imagine getting cables there is a hassle?

- Air conditioning/ASHP/MHVR? Noisy devices, but they typically need 'outside access' and short pipes, so putting them in a basement might decrease their efficiency?

- Freezer? Basements are cold, so efficient, but is it a drag to go up and down the stairs carrying food?

- Washing machine? Noisy but carrying them up/down extra stairs is a hassle?

- Guestrooms? Kid Rooms? Quiet, but no light gets you down?

- Showers/Bath/Sauna? Getting wastewater out is a hassle?

 

Cost vs size and other factors: 

- What would be the cost of a 1m2 basement (meaning: are there any costs you always have to pay?)

- Full house size saves on some costs but at the end of the day is serious £££ - I doubt you can get it below 1000?

- In NL, it's quite common to create a crawlspace rather than a basement. Basically a 1m high unfurnished basement allowing easy access for plumbing etc.

- Furnishing - if we assume an 'empty hall' (with the necessary weight supports) is 1000/m2, how much  would making it 'proper rooms with all the normal, not excessive trimmings'?

-> what can we do to minimize basement cost?

 

Position:

- As I understand it, neighbours might not like 'basement building activities' very near to their property(line). not sure why? Is there a risk that a basement cut too close to the neighbours will unhinge their property? 

- Am I correct heating/cooling gear strongly benefits from being right next to a wall? Or is it fine to get a reasonably short duct (2-3m?) for whatever heat/gas/air needs to go in and out?

 

Edited May 8, 2020 by puntloos

[Thorfun]

I look forward to reading peoples responses to this! Following with interest...

[Conor]

We're building a full footprint basement as part of our project. We looked at various scenarios (split level, partial basement, no basement but bigger footprint) and the full basement came out best value for money. I think I calculated it as an extra £400/m² compared to standard ground floor build, but we get an extra 100m² of space.

 

- we have a limited footprint to work with, in order to get a 4 bed house, we either need a bedroom on ground floor or in a basement. 

- we are on a sloping site, so have to deal with a 1.5m fall from front to back of house regardless.

- rear aspect of basement will be at ground level

- we will have a utility/laundry room, plant area, cold storage room, plus a large "store" that could be used as a gym/play room/study etc in future- no money for that now but have included an escape window at least.

-hope fully having a dumbwaiter (3£k) from 1st floor to laundry room. Otherwise navigating two flights of stairs with laundry baskets would be unnaceptable for my partner (mobility issues)

- costs have come back and raw construction cost is about £10k more than building the same 100m² at ground level - about £6k of that is tanking and £4k ground works. It's a standard concrete raft with ICF walls- exactly that same as if it were at ground level.

-expect to be another £5k of additional costs in form of extra retaining walls and drainage/landscaping costs. We will be able to have a (sparce) completed basement at passive standard for less than £1k/m²

-Our heat pump will be approx 10m from the plant Room.... As long as the pipework is internal, right diameter and insulated, it doesn't matter really.

-mvhr is having to go in a hallway as needs to be on an external aspect wall.

-to save money and embrace the basement feel... We aren't having suspended ceilings, walls will be painted block, (ICF walls will be lined with ply) electric fittings will be surface mounted, floor will be poured resin or vinyl. No skirtings etc.

[Pocster]

Hey!

 

I have my basement constructed and it will be a fully liveable area.

 

You need to consider ground structure. We were in solid virgin rock and although council and neighbours bitched it wasn't much of an issue 1100tons from memory.

Admittedly I did all the work myself ( apart from the excavation ) - so my costs are rock ( no pun intended ) bottom.

The extra space though at extra cost depends on the 'wealth' of your neighbourhood and value of a standard property.

I used the concrete lego blocks to build the retaining walls ; with rebar in them and then just one concrete pour for the entire lot.

 

Basement issues as you state will be ventilation - but MVHR solves that anyway.

Macerator to pump waste/foul up to drain - no real big issue there.

 

Our kitchen will be underground so yes carrying food/washer/freezer down there will be a pita.

I've got a dumb waiter - she's called SWMBO ( don't ever repeat that or I'll be stabbed in my sleep ).

 

Costs?. Depends how much you are willing to do I guess.

 

I presume you are adding a basement to an existing house not building the entire thing from scratch?? 

Edited May 9, 2020 by pocster

[tonyshouse]

Ten years ago my basement including the g/f slab but not finishes cost 35k and was 80m2 

[Bitpipe]

Deep breath

 

So we decided to have a basement and as the plans evolved it grew from 1/4 to 1/2 to full footprint. Planners didn't blink - represented about 50% extra floor space.

 

As we're in clay / gravel / chalk we anticipated that the foundations would need to be deep anyway (based on a next door's extension, he had to go down 2m of clay) so the cost of the basement structure could be offset against traditional foundations / slab.

 

From a design point of view we originally made it a big open box. Decided on suspended timber floor vs concrete lid as we wanted the basement to be part of the passive envelope and to have wet UFH under the suspended timber.

 

Basement costs are variable and can't be assessed until you have done ground investigation - best if the scope of study is defined by your SE otherwise you may not get key info you need.

 

The ground conditions are the big question - what are you sitting on, how hard will it be to get it out, how much will there be to get rid of (different things bulk up differently) and how will it impact the basement design.

 

Site conditions are next most important -- how tight is your site, how close to neighbours, ease of access to plant etc.

 

If you get PP, your neighbours cannot stop you building a basement, but you will need to respect the party wall regulations. If you are close to their properties, you'll need to take necessary precautions and may have to resort to sheet piling etc which all add ££.

 

Function wise, ours is about 110m2 internally. It's been chopped into four rooms, two are TV /music rooms / dens for the teenagers and the other two are a gym (more boxes than gym kit) and a craft room (full of junk and tools) and then the plant room for MVHR, UVC, power distribution & gas boiler.

 

We were reluctant to put loos etc down there, there is a WC on the GF so not a hardship to come up to use that. We put our old fridge freezer and a cabinet freezer down there and handy for xmas and during the lockdown. 

 

Don't want to use any of it for bedrooms per se, but it is classed as habitable space by BC and complies with the necessary fire regulations as it has an independent exit to outside.

 

Cost for the shell was probably £100k - was part of a £120k package for demo of existing and services, fouls etc.

 

Fit out was not that much in grand scheme - electrics, plastering & joinery. We were prepared to defer that if the budget got squeezed but we were ok - economies of scale helped as there are 2.5 floors above the basement that all needed the same.

 

Really happy we did it - gained us 50% extra floor space for maybe 20% additional spend.

[Thorfun]

1 hour ago, Bitpipe said:

Cost for the shell was probably £100k - was part of a £120k package for demo of existing and services, fouls etc.

 

did you ever get quotes for the foundations without the basement? if not, any idea how much the foundations would've been?

 

therefore the extra cost of the basement would be £X as you would've needed the foundations anyway.

[puntloos]

5 hours ago, Conor said:

We're building a full footprint basement as part of our project. We looked at various scenarios (split level, partial basement, no basement but bigger footprint) and the full basement came out best value for money. I think I calculated it as an extra £400/m² compared to standard ground floor build, but we get an extra 100m² of space.

 

And how much was standard ground floor build? If it was 100/sqm then a basement at 500/sqm doesn't sound good

 

 

5 hours ago, Conor said:

- we have a limited footprint to work with, in order to get a 4 bed house, we either need a bedroom on ground floor or in a basement. 

So this means you had neighbours close?

 

5 hours ago, Conor said:

- we are on a sloping site, so have to deal with a 1.5m fall from front to back of house regardless.

 

Which would presumably increase your base 'foundation' cost a bunch?

 

5 hours ago, Conor said:

- rear aspect of basement will be at ground level

- we will have a utility/laundry room, plant area, cold storage room, plus a large "store" that could be used as a gym/play room/study etc in future- no money for that now but have included an escape window at least.

-hope fully having a dumbwaiter (3£k) from 1st floor to laundry room. Otherwise navigating two flights of stairs with laundry baskets would be unnaceptable for my partner (mobility issues)

- costs have come back and raw construction cost is about £10k more than building the same 100m² at ground level - about £6k of that is tanking and £4k ground works. It's a standard concrete raft with ICF walls- exactly that same as if it were at ground level.

-expect to be another £5k of additional costs in form of extra retaining walls and drainage/landscaping costs. We will be able to have a (sparce) completed basement at passive standard for less than £1k/m²

-Our heat pump will be approx 10m from the plant Room.... As long as the pipework is internal, right diameter and insulated, it doesn't matter really.

-mvhr is having to go in a hallway as needs to be on an external aspect wall.

-to save money and embrace the basement feel... We aren't having suspended ceilings, walls will be painted block, (ICF walls will be lined with ply) electric fittings will be surface mounted, floor will be poured resin or vinyl. No skirtings etc.

 

And the final question: this is in Holywood Ireland? No idea how to work the price in there..

 

2 hours ago, pocster said:

Hey!

 

I have my basement constructed and it will be a fully liveable area.

 

You need to consider ground structure. We were in solid virgin rock and although council and neighbours bitched it wasn't much of an issue 1100tons from memory.

 

So what would be the 'cheapest' ground structure? I do understand that the underground water level matters a lot, but I assume you mean "clay" vs "gravel" vs "basalt"..

 

 

2 hours ago, pocster said:

Admittedly I did all the work myself ( apart from the excavation ) - so my costs are rock ( no pun intended ) bottom.

 

So how much was the excavation then? As I understand it this is an important part of the total cost... trying to wrap my head around how much it would cost here..

 

2 hours ago, pocster said:

The extra space though at extra cost depends on the 'wealth' of your neighbourhood and value of a standard property

Very good point, I think we are kind-of maxing out the price of our house after all's built. Adding a basement will be 'cool' but not sure if it'll yield more.. although perhaps I can address the evil geniuses ('Comes with an underground lair!') market.. hmm

 

2 hours ago, pocster said:

I used the concrete lego blocks to build the retaining walls ; with rebar in them and then just one concrete pour for the entire lot.

 

Basement issues as you state will be ventilation - but MVHR solves that anyway.

Macerator to pump waste/foul up to drain - no real big issue there.

 

Our kitchen will be underground so yes carrying food/washer/freezer down there will be a pita.

 

Huh, interesting choice, why this? No space upstairs?

 

2 hours ago, pocster said:

I've got a dumb waiter - she's called SWMBO ( don't ever repeat that or I'll be stabbed in my sleep ).

SWMBO! 

 

(please report back)

 

2 hours ago, pocster said:

Costs?. Depends how much you are willing to do I guess.

 

Pretty much nothing. Make an occasional coffee..

 

2 hours ago, pocster said:

I presume you are adding a basement to an existing house not building the entire thing from scratch?? 

 

Entire thing from scratch!

 

1 hour ago, tonyshouse said:

Ten years ago my basement including the g/f slab but not finishes cost 35k and was 80m2 

 

Thames Valley.. hmm might be comparable to my pricing (herts)..

 

 

34 minutes ago, Bitpipe said:

Deep breath

 

So we decided to have a basement and as the plans evolved it grew from 1/4 to 1/2 to full footprint. Planners didn't blink - represented about 50% extra floor space.

 

As we're in clay / gravel / chalk we anticipated that the foundations would need to be deep anyway (based on a next door's extension, he had to go down 2m of clay) so the cost of the basement structure could be offset against traditional foundations / slab.

 

We're in clay-only here.. is that good or bad? ?

 

34 minutes ago, Bitpipe said:

From a design point of view we originally made it a big open box. Decided on suspended timber floor vs concrete lid as we wanted the basement to be part of the passive envelope and to have wet UFH under the suspended timber.

 

Basement inside envelope seems sensible enough, I'm not a massive fan of wooden floors (creaky..) but perhaps something a bit more passive-suitable happiness through chemicals is doable.. what's the ideal UFH floor anyway.. I thought it was some type of resin/vinyl/laminate.. 

 

 

34 minutes ago, Bitpipe said:

Basement costs are variable and can't be assessed until you have done ground investigation - best if the scope of study is defined by your SE otherwise you may not get key info you need.

 

The ground conditions are the big question - what are you sitting on, how hard will it be to get it out, how much will there be to get rid of (different things bulk up differently) and how will it impact the basement design.

 

Site conditions are next most important -- how tight is your site, how close to neighbours, ease of access to plant etc.

 

If you get PP, your neighbours cannot stop you building a basement, but you will need to respect the party wall regulations. If you are close to their properties, you'll need to take necessary precautions and may have to resort to sheet piling etc which all add ££.

 

Function wise, ours is about 110m2 internally. It's been chopped into four rooms, two are TV /music rooms / dens for the teenagers and the other two are a gym (more boxes than gym kit) and a craft room (full of junk and tools) and then the plant room for MVHR, UVC, power distribution & gas boiler.

 

We were reluctant to put loos etc down there, there is a WC on the GF so not a hardship to come up to use that. We put our old fridge freezer and a cabinet freezer down there and handy for xmas and during the lockdown. 

 

Don't want to use any of it for bedrooms per se, but it is classed as habitable space by BC and complies with the necessary fire regulations as it has an independent exit to outside.

Might be a fun AirBNB (or Mother in Law) option at some point

 

34 minutes ago, Bitpipe said:

 

Cost for the shell was probably £100k - was part of a £120k package for demo of existing and services, fouls etc.

 

Not sure I understand, do you mean your entire shell, even if you didn't have a basement?

 

34 minutes ago, Bitpipe said:

Fit out was not that much in grand scheme - electrics, plastering & joinery. We were prepared to defer that if the budget got squeezed but we were ok - economies of scale helped as there are 2.5 floors above the basement that all needed the same.

 

Yeah I imagined. Main cost I assume is making it watertight and actually getting the sand out of there

34 minutes ago, Bitpipe said:

Really happy we did it - gained us 50% extra floor space for maybe 20% additional spend.

 

That's at least a ratio I could live with.. my current rule of thumb is 2000*250m2 = 500000 - if I can get 375 for 600000 I might... might.. consider it if the gods of finance allow it..

 

 

[Bitpipe]

1 hour ago, Thorfun said:

 

did you ever get quotes for the foundations without the basement? if not, any idea how much the foundations would've been?

 

therefore the extra cost of the basement would be £X as you would've needed the foundations anyway.

 

Yes, got quotes for a passive slab - £20k + the groundworks which would have been £5k probably including stone etc - not sure, never priced that side up.

 

So additional basement structure cost was £75k.

 

That said, the suspended timber floor was extra (steel, joists and OSB deck). We could have created a six sided box and probably used the same amount of concrete and  steel (as walls would have been 200mm vs 300mm.

 

I didn't mention waterproofing above - another key consideration based on your ground conditions. As we had GW at 6m and the basement excavation was 3.5m we were allowed to just have warrantied waterproof concrete so that was quite cost effective. External tanking membranes or internal pump & sump all add cost and complexity.

 

 

[Pocster]

7 minutes ago, puntloos said:

So what would be the 'cheapest' ground structure? I do understand that the underground water level matters a lot, but I assume you mean "clay" vs "gravel" vs "basalt"..

 

 

No idea!. I assume rock as it would require no shuttering to support the hole!. You need to do some ground tests anyway - council would require that.

 

 

8 minutes ago, puntloos said:

So how much was the excavation then? As I understand it this is an important part of the total cost... trying to wrap my head around how much it would cost here..

 

 

17.5k. That's to dig out and take away. The guy who dug it out was also an aggregate recycler - so he'd turn the rock into chippings...

 

8 minutes ago, puntloos said:

Huh, interesting choice, why this? No space upstairs?

 

 

Yeah of course we do. But my neighbours are all twats and I couldn't get around planning with a 2 storey house (even though all the surrounding houses are ) - underground no one can complain!

 

8 minutes ago, puntloos said:

Entire thing from scratch!

 

Get going then!. It's SOME work !!

[Bitpipe]

Can I just say the mega quoted response makes it a bit hard to respond in context but I'll do best!

 

I'm just down the road from Tony in Berkshire, he did the work himself and is very knowledgable so you'd be pushed to get close to his numbers using contractors.

 

2 hours ago, puntloos said:

We're in clay-only here.. is that good or bad? ?

 

 

Your SE will dictate how the build conditions determine the structure but my understanding is that with clay, you need to keep going down until you hit something solid enough to take the load without future movement. May need piling - SE will tell you.

 

While you need your own customised ground report, you can sometimes find historical surveys logged on the British geological society website and do a guess what you may be on.

 

2 hours ago, puntloos said:

Basement inside envelope seems sensible enough, I'm not a massive fan of wooden floors (creaky..) but perhaps something a bit more passive-suitable happiness through chemicals is doable.. what's the ideal UFH floor anyway.. I thought it was some type of resin/vinyl/laminate.. 

 

Not sure what you mean here. Our basement slab sits on 300mm of EPS 200 which extends out beyond the slab edge. Then there is 200mm EPS applied to the exterior of the basement wall. This meets the insulated layer of the MBC passive frame with the load bearing leaf sitting on the top of the basement wall.

 

Our 'wooden floor' is a steel web socketed into 100mm pockets on the basement walls. Between steels are pozi joists. On that is 18mm OSB, glued & screwed. On this is cross laid 12mm and then 9mm marine ply, glued & nailed. On top of this is a rubber crumb and then a poured resin floor. Not creaky.

 

2 hours ago, puntloos said:

 

Might be a fun AirBNB (or Mother in Law) option at some point

 

 

Be wary of using basement space for sleeping accommodation, I think this further complicates either building or planning regs. You'd also need bathroom facilities down there which complicates things.

 

2 hours ago, puntloos said:

Not sure I understand, do you mean your entire shell, even if you didn't have a basement?

 

 

Basement shell - the concrete structure minus any finishes or services inside. 

 

Cost of excavated material depends on what it is. If it's easily removable with a big enough machine (i.e. not rock) then the cost is usually per M3. However getting rid of it (muck away) depends on what the Waste Acceptance Criteria  testing says (you want inert, anything else is very expensive) and how it bulks up as the 20t wagons are also limited by volume.

 

Chalk is worst (bulks up 3:1), clay is about 2:1 and stone, gravel etc is 1:1

 

Your contractor will also have to excavate a working area of 1m from the face of the external wall and batter back the sides for stability. This can lead to a very large hole and if close to neighbouring properties you may need to sheet pile.

 

Your spoil may not be suitable for backfill (ideally you want something non compressible with good percolation like large (fist sized) stone.

[puntloos]

Just reviving this for a second. 

 

Anyone have a rough quote for:

 

- 3x3 basement.

- Only for heating equipment

- Simple stair into garage

 

My current quote from one builder is 72000 GBP but it feels this is pretty.. pessimistic

[Thorfun]

24 minutes ago, puntloos said:

Just reviving this for a second. 

 

Anyone have a rough quote for:

 

- 3x3 basement.

- Only for heating equipment

- Simple stair into garage

 

My current quote from one builder is 72000 GBP but it feels this is pretty.. pessimistic

 

£72k for a 3x3m basement! holy cr@p that's a lot. I'd be looking to build a shed instead.

 

doesn't bode well for when I get my basement priced up.

[puntloos]

Just now, Thorfun said:

 

£72k for a 3x3m basement! holy cr@p that's a lot. I'd be looking to build a shed instead.

 

doesn't bode well for when I get my basement priced up.

The main point they were making is that for a small basement the 'start up costs' are steep. The larger you go the cheaper per sqm.. but yep, that's what I heard.

[Thorfun]

2 minutes ago, puntloos said:

The main point they were making is that for a small basement the 'start up costs' are steep. The larger you go the cheaper per sqm.. but yep, that's what I heard.

 

if it's under an existing garage then I can understand steep costings due to underpinning and digging out under an existing structure but £72k to dig a hole and waterproof it seems crazy. 

I wish you all the best with it.

[Pocster]

10 hours ago, Thorfun said:

 

if it's under an existing garage then I can understand steep costings due to underpinning and digging out under an existing structure but £72k to dig a hole and waterproof it seems crazy. 

I wish you all the best with it.

That price seems WAY to high !

I got 20 quotes ( just to excavate and take away ) they ranged from 7k ( way too cheap ! ) to 100k !!!

[puntloos]

13 hours ago, pocster said:

That price seems WAY to high !

I got 20 quotes ( just to excavate and take away ) they ranged from 7k ( way too cheap ! ) to 100k !!!

 

For what size basement? Perhaps I should consider getting separate 'basement guys'... 

[Pocster]

10 hours ago, puntloos said:

 

For what size basement? Perhaps I should consider getting separate 'basement guys'... 

It was approx 18m x 8m 

1100 tons of rock .

I don’t know your ground structure but yes getting the hole dug and taken away as a seperate job would be cheaper .

Then you can choose another firm for ring beam / slab / retaining walls etc .

I had to dig my hole right next to a public lane - so that required the Lane always being open . My initial instinct was pile driving along that side - 22 piles at £1100 each !!! . So I found another substantially cheaper method .

[Thorfun]

10 hours ago, puntloos said:

 

For what size basement? Perhaps I should consider getting separate 'basement guys'... 

 

in this thread I started it was recommended not to go for a 'basement guy' as they'd likely slap some zeros on the end of the quote as they're specialists.

 

 

[tonyshouse]

Ten years ago my basement including g/f slab structure cost 35k 80m2 diy plus 50% of brickies and labourer and jcb

[puntloos]

Hrm yeah 35K is more like it

 

I wonder what gives, why this builder is so expensive (while they 'seem reasonable') on most other costs..

 

Anyone have a more recent job done near(ish) london?

[Simplysimon]

1 hour ago, puntloos said:

Hrm yeah 35K is more like it

 

I wonder what gives, why this builder is so expensive (while they 'seem reasonable') on most other costs..

 

Anyone have a more recent job done near(ish) london?

he's not too sure on what's required and is covering his ar$e

[Bitpipe]

If you want a sensible basement quote, talk to local (ish) groundworkers who build underground structures all day long. Not much difference in an underground carpark and a basement other than the finish.

 

They will manage heavy plant, excavation, muck away and reinstatement - likely they will sub out the concrete works and build whatever spec your SE has designed. They will also do all your services work, laying fouls, rainwater, fresh water, ducting for power and plant, site access, etc. 

 

A general builder will likely not have underground  experience beyond standard foundations, which they may well still sub out to a groundworker.

 

A basement company will certainly inflate the price, most of these firms specialise in basements under existing dwellings which is a different thing altogether.

 

If you have a clear site with decent access, a sound understanding of the underlying ground conditions and a sensible design from a SE then you should be able to approach most GWs for a quote. Make sure BC are happy with design inc. access and emergency exit / fire protection. If you don't have a separate exit from the internal stairs then you will need fire suppression such as sprinklers.

 

Expect prices to increase /sqm if the basement is small, access is difficult, neighbouring properties are close and you have challenging ground conditions such as weak ground, high water table or radon gas etc.

 

When you have the finished basement shell with house on top, you fit it out with the rest of the house.

 

I found very little of the 'domestic' building services (builders, architects etc) confident to deal with basements. However once I tapped into local GWs then I had lots of options.

 

Tip - if there are any large public works going on near you, see who the GW contractor is. 

 

But before you do ANYTHING - get a decent ground survey designed by a SE as that will drive all costs as you move forward. Maybe you spend the money and decide you can't afford to proceed but that's better than starting the job and finding nasty surprises that mean you can't afford to finish it.

 

[tonyshouse]

 

 

[Pocster]