Hello from London

[LadyBuilder]

Hi,

 

Brief intro from me. We have just gotten planning permission to build a house in Central London. It has been a year from plot purchase to planning permission, but overall I think it has gone well, despite the changing concept completely. Started off with building a modern house on one side of the plot, ended up with planning for a Victorian house on the other side of the plot.

 

Anyway, we are keen to be sustainable and energy efficient as possible, but have no need for certificates or accreditations.

 

I run a interior refurb company, so I am in the building trade, but don't have much experience with building whole houses (small extensions, one tiny basement, etc). However I have decided to do the entire build pretty much with my people in order to fit into the budget that we have. I'm lucky that being Bulgarian, I have access to cheap labour, but unfortunately most of it is rather unskilled. We have an architect and structural engineer, but the rest I am doing pretty much myself. Which is a very daunting task and I will need all the help I can get.... hence this forum.

 

We tried to keep the house as simple as possible. Large rectangular basement, two square floors on top and a liveable roof space. The basement is contiguous piles and a concrete box with a concrete ground slab. The house after that is either SIPs or ICF with a SIPs roof. I am really struggling with that decision. If SIPs, I have a great price, they come and do everything for me in 4-6 weeks. If ICF, I’ve got to get the know how and do it all myself with a bunch of guys who will expect directions and wisdom from me. However, I can’t help but think that ICF is more ‘robust’/long life solution to SIPs… Any advice appreciated!

I am also struggling with all the decisions like MVHR or not (timber sash windows in a conservation area), air source pump or really good gas boiler etc. Finding suppliers for the thousand things I need is also a full time occupation.

Anyhow, we start piling in January (I still haven’t got the Party Wall award or the water installed) and I need to sort out the drainage before anything else. Thoughts on connecting basement floor directly to sewer (what if it overfloods) or preferable to use sumps (maintenance, electricity and costs of materials!)?

[ragg987]

Hi there, welcome and seems you have an interesting project here.

 

There are others here who will chip in with more experience - I can only come at it based on our own build so a little "one-dimensional".

 

Basement - we looked at various options and decided to go ICF with waterproof concrete and joints. The slab of the basement sits on polystyrene. I kept all wet services out of our basement to keep it simple - hence no need for secondary water-related considerations like pumps, tanking etc, just a small drain in the lightwell for rainwater.

 

For the main house, do take a look at MBC timberframe, especially if your objective is a low-cost thermally efficient house. I was advised against SIPS by my architect and project manager for reasons I do not recall. If going ICF I suggest you (or your builders) think about attending some courses that the specialists can provide.

 

I feel MVHR is essential - it will save energy as well as keep the interior well ventilated. The key is to ensure you have built as air-tight a box as you can by using membranes, attention to detail with sealing doors, windows and other service holes.

 

If you have mains gas then I think use that rather than ASHP. Cheaper to fit and not much difference in running cost.

[LadyBuilder]

Thanks for your reply. I looked into ICF in the basement but decided against it. My worry was that if any joints are not done well and I get a leak/crack, it would be very difficult/expensive to find. I plan on using bentonite geotextile as my first form of water defence in the basement as it allows me to blindside waterproof on the piles.  I am also currently exploring shortcrete for the walls. the idea of simply attaching the mesh to the piles and spaying appeals a lot. Unfortunately it is not so popular so not many people can advise...

 

I've just send off for a quote with MBC, I hadn't really heard of it before coming to this forum.

 

Given that I will have timber sashes, my worry is that they will not be airtight at all and the MVHR will not do much but waste electricity. I have to say that the size of the house is the main problem in making all these decisions. At 6200 sq feet, I need 2 of everything and it becomes rather expensive

 

 

[ragg987]

"Air-tight sash" (no experience with these, random google search)

https://www.greenbuildingstore.co.uk/products/triple-glazed-timber-sliding-sash/

 

We used Kryton waterproofing for the basement. The theory is that any water ingress through small cracks will activate the Kryton and it will expand to fill the crack. Self-healing. The installation was inspected, certified and warranted by Kryton.

 

6200 sq ft should be doable with a single commercial-oriented MVHR, though if your house is long and thin it could well be more efficient to get 2 separate units to avoid long runs of duct. Suggest you speak to BPC, knowledgable and great prices. A single large gas-boiler should also suffice, depending on number of occupants and hot water demands a single large DHW cylinder might suffice, maybe add a pump to circulate hot water around.

 

Hope you have planed for a plant room for all this stuff!

[ragg987]

Kryton video, it keeps the fish out!

https://www.youtube.com/watch?v=iwp7Xe1wW9U&feature=youtu.be

[LadyBuilder]

I have a 3200sq feet basement that I have no idea what to do with, so plenty of room for any plants :-) (Yes, have a plant room planned)

 

I am not familiar with Kryton, will do some research. I used this one my previous basement:

 

http://www.premcrete.com/solution/maxi/

 

I'm also adding the plans as always useful to hear knowledgeable people's opinions

 

 

DR 02_BASEMENT PLAN.pdf

DR 03_GF PLAN.pdf

DR 04_UPPER FLOORS AND ROOF.pdf

[le-cerveau]

1 hour ago, LadyBuilder said:

I looked into ICF in the basement but decided against it.

 

The question is how are you going to insulate your basement, you ideally want to insulate outside the concrete to avoid/reduce thermal bridges.  This is where ICF comes in as it forms the insulation and the former for pouring the concrete, subterranean you still have to waterproof outside the ICF with an appropriate tanking layer.

[LadyBuilder]

Good point, this is how I ended up on this forum actually... researching under or over slab insulation.

 

At this point my thinking is insulation on the inside. I did this last time and worked well, but would be keen to hear people's opinions of efficiency of insulation. This method allows me to have the bentonite as type A and then the membrane as second form of defence. Opinions?

 

[jack]

Welcome to the forum.

 

I take it you've had a look at the basement sub-forum? Not many posts, but @Bitpipe's provide quite a bit of detail about what he ended up doing.

[Bitpipe]

Hi, did someone say basement

 

We built a passive*  'cast in situ' basement made of Sika warrantied waterproof concrete in Berkshire and then popped a MBC passive standard house on top. 

 

*essentially sits on 300mm of EPS250 with 200mm EPS70on the sides to meet the insulated layer for the MBC house.

 

Very happy to bore you senseless on the details.

 

Also looked at ICF all the way but it was much more expensive than the option we ended up going for TF.

[LadyBuilder]

Just been reading your posts re basements.

 

it appears that you had a lot more room than me. Being in Central London, space is at a premium, so I am piling on the boundaries. This essentially means that even the formwork needs to be one-sided. Hence my interest in shotcrete...

 

I hear lots of talk about WPC, but my worry is that it is only as good as the people doing the formwork/pour. Using my guys, I don't believe I would be able to guarantee the quality. Using anybody else will be giving away a lot of money (self build in london means 'i'm rich&stupid and I am looking to find someone to rob me blind') Had quotes for the basement box only!!! (not waterproofing or services) between 400k and 600k

 

here is a birdseye view of basement plan

17127-PL.01-P1_Basement_Plan.pdf

[Bitpipe]

First things first - what did your ground survey say re-water table? Are you above it or in it? We're above ours so went for 

 

The design above is not that great as it assumes that the basement will leak and you're effectively building a membrane inside the basement to catch water and take it to a sump, which needs a pump (and a spare or alarm etc...). Works well for retro basements but you can do better.

 

Sika, Kryten or similar will give you a warrantied watertight box, assuming that the crew are trained and licenced to use that system. The waterproof reps will come to inspect work and sign it off to generate the warranty.

 

External membrane is optional - I didn't bother. Warranty provider was fine with that.

 

To insulate, we laid 300mm EPS 250 (as approved by the SE, you may need higher/lower spec depending on the weight of your structure) on a 150mm blinded base and then put some Radon membrane over the top. The basement crew treated this as ground zero and laid the rebar on top and made the slab with a 100mm kicker. Then each wall section was cast in situ with penetrations made for lightwells, door to external means of escape and services. Sika waterproofing bar & mastic at every join and the holes left by the shuttering support bars were plugged with a rubber bung that screws tight to the hole sides

 

We designed an 'open box' basement which meant stronger walls (effectively cantilevered) and then had a steel & suspended timber floor vs a poured lid. Cost wise it was probably marginal but gave us more flexibility on the internal layout (which we framed in timber).

 

MBC did not blink when we suggested doing a house over a basement and I think they're still in touch with the contractor we used if other clients requested similar. 

 

Design wise, MBC did the house design first and then we passed everything to the SE who designed the basement & steel floor to match up, we then passed this design back to MBC who took care of the steel & timber ground floor and another contractor did the basement construction.

 

I was quite nervous about the whole thing coming together but needn't have worried as MBC took final measurements off the finished basement before putting the frame into production.

 

If you go for a more traditional cast lid then it can be treated just like a slab foundation but you will need to make sure point loads are catered for.

 

MVHR is a must, cheap as chips in the grand scheme of things - superior ventilation and significantly reduces your energy bills through efficient heat recovery. You can turn it off, open windows if you wish (although you'll want windows without trickle vents).

 

The only other reason I was wary of ICF is that you can't inspect the pour quality, which if that's all you're relying on is a bit of a leap of faith.

 

 

[LadyBuilder]

we encountered water at 3.5m but this is deemed as short term standing water and most likely perched water sitting at the top of the London Clay

 

i am still not certain what is the benefit of having the insulation under the slab vs over. the basement will not be used a lot, i am thinking it is better for the ufh to not heat the slab given it size. I want to be able to heat the rooms quickly, rather than use a lot of energy to warm up the slab for only a couple of hours use every other day

[ragg987]

8 minutes ago, Bitpipe said:

The design above is not that great as it assumes that the basement will leak and you're effectively building a membrane inside the basement to catch water and take it to a sump, which needs a pump (and a spare or alarm etc...). Works well for retro basements but you can do better

My feeling exactly. Three lines of defense which adds expense and assumes one or the other will fail.

 

Our approach was similar, apart from using ICF formers to insulate inside and out, plus we had a beam and block roof over which MBC build their structure.

[LadyBuilder]

I will contact Sika to get a price, but the prices of WPC here like Caltite etc are almost double to other concrete. Which in my case would would out to an extra £35k roughly

[LadyBuilder]

I have to have a sump for the lightwells anyway, as the combined sewer is above basement level. I might getaway with the foul pipe running above the slab or in it (not very keen) but given the span, no way for the lightwell

[Bitpipe]

2 minutes ago, LadyBuilder said:

we encountered water at 3.5m but this is deemed as short term standing water and most likely perched water sitting at the top of the London Clay

 

i am still not certain what is the benefit of having the insulation under the slab vs over. the basement will not be used a lot, i am thinking it is better for the ufh to not heat the slab given it size. I want to be able to heat the rooms quickly, rather than use a lot of energy to warm up the slab for only a couple of hours use every other day

 

As we had a passive house design, I needed a full wrap of insulation around the house.

 

I have no heating in the basement and it's fine, even in this subzero spell we're having. A few humans and gadgets, plus the plant room,  kick out enough heat to make it more than comfortable.

 

BTW, if your crew are very unskilled then I'd be wary having them build the basement without some supervisory expertise as any mistakes may turn out to be very expensive later. 

 

[ragg987]

Insulation under slab is your primary defense against heat loss to the ground. ICF gives insulation inside and outside, but much less inside than out so it still allows the slab to absorb the heat and this will create a stable temperature with minimal need for additional heat.

 

The key here is getting the right level of insulation in which case your heating requirement is very small. Ground temp is generally quite stable at about 8-10C, so heat loss will be much smaller than above ground. Unless you have moving water.

 

For lightwells, you may not need a sump - maybe drain it to a small soakaway which can be catered for during the basement dig, you would not expect much water ingress into a small opening.

[LadyBuilder]

They are not very unskilled, I just could not guarantee that there will not any hairline cracks in a 72m long perimeter wall 3m high (which ideally should be done as stage pour)

 

basement is is the games, guest room, gym, etc so I prefer to have heating. given it's size, I might turn it into a kids birthday party area i my husband ever agrees

[LadyBuilder]

My london clay has been deemed unsuitable for infiltration suds, hence the permission to join the combined sewer. We are on a slope, so I expect surface water from above in an area classified as 'critical drainage' by the council

 

Interestingly, I was reading that ground source pumps and they draw heat from the soil. There is a significant diffrence between the surface temp of soil and the temp 3m below. a study was done to show that when surface soil temp is 2.5 degrees, 3m below is around 11.5. That leads me to believe that less insulation is needed in basement slabs vs ground slabs and generally heat loss at basement level is not the same issue as at ground level

[LadyBuilder]

Essentially, I don't mind where I put the insulation, above or below. I will not be able to use bentonite if it is below, so then I have to use WPC, which is more expensive than the bentonite

[ProDave]

2 hours ago, LadyBuilder said:

I have a 3200sq feet basement that I have no idea what to do with, so plenty of room for any plants :-) (Yes, have a plant room planned)

 

Okay I will ask the daft question.

 

If you have no plans for the basement, then why build one? it's not as though it is cheap additional pace is it?

[LadyBuilder]

Ha ha, I do have plans... but there is still quite a lot of space that I don't know what we'll do with.

 

I live in Nappy Valley, so one idea is to create a birthday party venue for children as there is nothing similar around, but my husband is not keen...

 

We decided to build as big as we can, as adding extra basement afterward is not cheap. 3 kids, loads of relatives from overseas... you never know

[Ferdinand]

55 minutes ago, LadyBuilder said:

Just been reading your posts re basements.

 

it appears that you had a lot more room than me. Being in Central London, space is at a premium, so I am piling on the boundaries. This essentially means that even the formwork needs to be one-sided. Hence my interest in shotcrete...

 

I hear lots of talk about WPC, but my worry is that it is only as good as the people doing the formwork/pour. Using my guys, I don't believe I would be able to guarantee the quality. Using anybody else will be giving away a lot of money (self build in london means 'i'm rich&stupid and I am looking to find someone to rob me blind') Had quotes for the basement box only!!! (not waterproofing or services) between 400k and 600k

 

here is a birdseye view of basement plan

17127-PL.01-P1_Basement_Plan.pdf

 

There was recently a Grand Designs in East London where they had a disastrous contractor for their basement, who they then replaced with somebody competent.

 

Perhaps you could find the competent replacement.

 

Episode here with link to supplier list:

https://www.granddesigns.tv/east-london/

 

Since that whole site was 38sqm, presumably they would find yours spacious.

 

[LadyBuilder]

I have actually spoken to the basement guy who did the first bit... ages ago when I was doing my first basement. I did it with my guys (luckily, judging from the show)

 

I also spoke to the competent replacement, but all the quotes are in the region above.