Oz07 Posted December 12, 2017 Share Posted December 12, 2017 Think you'd be daft not to build a basement in London. If there are investors having basements dug and built below existing properties then that shows you how valuable space is! Sq footage is king Link to comment Share on other sites More sharing options...
Ferdinand Posted December 12, 2017 Share Posted December 12, 2017 (edited) @LadyBuilder Since you seem to know pretty well how to go about it, just a check are you on top of the self-build CiL exemption? In London there is a lot of CiL. Ferdinand Edited December 13, 2017 by Ferdinand Link to comment Share on other sites More sharing options...
LadyBuilder Posted December 12, 2017 Author Share Posted December 12, 2017 You are absolutely right, CIL is £214k... Got the cil exemption on fri, commencement notice sent yesterday.. spent most of today getting warranty quotes as i cannot get a self build mortgage but you are wrong, I still haven't got a clue what I am doing... so many options, so many pro and cons - frightening. some I've done before, some I've only read about and most of all a lot of things seems to be put in place as 'insurance', hence you never know if you need it or not, e.g. 2 forms of water defence - are drain cavities and membranes needed or just 'in case' water comes through my piling is 'in case' the excavation collapses metal deck for ground slab, supposedly safer than formwork etc etc Link to comment Share on other sites More sharing options...
Ferdinand Posted December 12, 2017 Share Posted December 12, 2017 I think the single most important point I would make is to take your time to get it right. It is a big project, and you have a fair bit of time on your Planning Application left, judging by the above. Link to comment Share on other sites More sharing options...
Bitpipe Posted December 12, 2017 Share Posted December 12, 2017 5 hours ago, LadyBuilder said: 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 My build is 400m2 and the Vent Axia Sentinel Kinetic Plus unit I have (about £2k ish) would easily support your build. Usual challenge is trying to centrally locate it to equalise duct runs as much as possible but I broke that rule by having it on one side of the basement and I've been able to balance it fine. Standard MVHR units use very little electricity, beyond a certain airtightness level they will not be efficient at recovering heat but this is usually a challenge in refurbs, not new builds. If you're serious about maximising your energy performance then you want to consider airtightness as much as insulation - you don't need to be striving for passive standards to have good airtightness to minimise heat loss. MVHR then becomes the most effective and efficient way to ventilate a space that has good airtightness. Regarding basement insulation, I had to go for external as I needed to replicate the MBC passive slab design. If your construction method negates that then inside is fine, just do the calcs to see what you need to hit the desired u value. Keep in mind that although the ground has a higher min temp compared to the outside air, it is more conductive so insulation is still required. You'd be surprised how little heat you need to inject into a well insulated airtight space (and basements are inherently airtight) to make it comfortable. Nearly everyone on this forum is challenged with keeping their build cool in summer vs warm in winter. That said, a few strategically placed electric wall panel heaters can be used in your basement - best strategy is to run the wiring for these and only install if you feel the need. You seem to have some experience in building basements so I probably can't add much more. That Newton system is not cheap but if you go for it (from memory) I don't believe you need an exterior membrane as you're assuming that the wall is inherently leaky to begin with. From that pov, ICF may be a good way forward as the skill level is low (many DIY it) and you wont be concerned about getting a perfect pour. Back in 2015 I was quoted £120/m3 for standard and £200/m3 for Sika waterproof (this was to supply & place, the raw material cost obv. lower). Link to comment Share on other sites More sharing options...
LadyBuilder Posted December 12, 2017 Author Share Posted December 12, 2017 For WPC I am getting £180+vat/m3 just for raw material, hence my reluctance to use. I am not so keen on Newton products, I prefer Delta, but I find Newton's techical drawings very good As I mentioned a few times, I am very keen to try shotcrete, got a £125+vat/m3 for raw material quote, but no formwork for the walls, so no worry in terms of bursts etc and considerable saving in terms of labour In terms of insulation, I'm so far thinking of either 200mm EPS/XPS (still researching if XPS worth the extra money) or 100mm PIR (CA4000)+ 50-60mm screed for the floor (gives me 0.11 u-value) and 100mm PIR (0.15 U-value) for the walls. Not sure how the PIR will be on a moist concrete floor, though I know people (builders) who swear it is absolutely fine I am tempted to put the bentonite and keep it without any membrane for the next 5-6 months, to see if any leaks. Then only do the membranes and perimeter drainage if necessary. the best quote I've had so far for MVHR is 10k for materials only. Your price is amazing! Are you ventilating every room or just wetrooms? I had a quote by panasonic for ASHP and they recommend 2 units (I asked them to quote for heating&cooling), I have to go back and ask why 2 units, it wouldn't make snse to need one unit for each component. I got a really good quote from a polish company for timber sashes (appr £700 a window), in previous jobs I've heard of nothing cheaper than 1.5k. So my thinking is that if air tight/triple glazed units cost 2k for example, it is better to get the polish and just use more heat... I've got something like 17 windows.... Link to comment Share on other sites More sharing options...
Onoff Posted December 12, 2017 Share Posted December 12, 2017 2 hours ago, Bitpipe said: beyond a certain airtightness level they will not be efficient at recovering heat but this is usually a challenge in refurbs, not new builds. Can you expand on that, I'm not understanding! Link to comment Share on other sites More sharing options...
SteamyTea Posted December 12, 2017 Share Posted December 12, 2017 I have only had a quick read of this, but my thoughts about the basement insulation are that you can fit it on the inside, it will not really make any difference thermally. Ground temperatures do not change too much over a year, so easy to calculate the losses. Then you can build your house on top with something similar to the MBC design, which is basically a timber frame house with a mixture of internal and external insulation. As far as I can work out, they do this to reduce thermal bridging when combined with the foundation design i.e. part of the house is thermally isolated by the slab design, the rest is thermally isolated by the Larson Wall. But too be honest, if you build the main house from block and added 300mm of insulation on the inside, it would be pretty cosy, though you could get nearly 400mm with a timber frame, so even better. I would not worry about your construction type too much. Just get some quotes and run the numbers about thermal performance. As you seem to have natural gas on site, go for that, your largest 'bill' will be domestic hot water, not heating (unless your cheap labour is really dreadful). MVHR is probably beneficial as you can keep more windows closed, reducing noise and dust, and increasing security (possibly). May even save something on the windows as less need to be opening. Your interior design is the thing that is going to add most value. Something that looks big is worth more in the capital than something that is bigger but feels cramped. See the conversation about small housing that @caliwag started. His idea of small and mine are different. The above is just mental rambling as without seeing the site and your plans, I can only comment on what is in my mind, not yours. Does sound a fun project and your Bulgarian works are probably easier to train and monitor than the shower of shit that is UK builders. Link to comment Share on other sites More sharing options...
Oz07 Posted December 12, 2017 Share Posted December 12, 2017 If going for mbc style twin wall wouldn't it be far more sensible to have external insulation on basement? Aren't you just introducing a cold bridge and/or painful detail otherwise? Link to comment Share on other sites More sharing options...
LadyBuilder Posted December 12, 2017 Author Share Posted December 12, 2017 I uploaded the plans in my third or fourth post. Not sure how to post as pics, only have pdf cheapest sip quote is appr 120k, icf is 24k but then I am not sure how to price all the other components: joists, roof, etc all of my quotes aim for around 0.13-0.15 U-value any idea how much the other stuff is for a cube that is 330 sq m? Link to comment Share on other sites More sharing options...
LadyBuilder Posted December 12, 2017 Author Share Posted December 12, 2017 (edited) 26 minutes ago, Oz07 said: If going for mbc style twin wall wouldn't it be far more sensible to have external insulation on basement? Aren't you just introducing a cold bridge and/or painful detail otherwise? I don't know, is the honest answer...all the basements I have seen (which is only in London) have the insulation inside My logic would be that the cold and hot air meeting inside rather than out may just result in condensation/damp, but then membranes are always installed as standard by all the builders I know Edited December 12, 2017 by LadyBuilder Link to comment Share on other sites More sharing options...
LadyBuilder Posted December 12, 2017 Author Share Posted December 12, 2017 (edited) 2 minutes ago, LadyBuilder said: My logic would be that the cold and air meeting inside rather than out may just result in condensation/damp, but then membranes are always installed as standard by all the builders I know and frankly concrete likes wetness/damp... as long it is not in the room and contained Edited December 12, 2017 by LadyBuilder spelling Link to comment Share on other sites More sharing options...
Bitpipe Posted December 12, 2017 Share Posted December 12, 2017 18 minutes ago, Oz07 said: If going for mbc style twin wall wouldn't it be far more sensible to have external insulation on basement? Aren't you just introducing a cold bridge and/or painful detail otherwise? It's essential for the twin wall system as the inner load bearing leaf of the twin wall sits on the outer edge of the basement wall and the outer (non load bearing) leaf sits on the outside edge to the basement insulation. When the void is pumped with cellulose, insulation meets insulation so there is continuity all around the building envelope. Not sure how you'd manage with the single wall MBC system (or equivalent or SIPs etc), potential of a cold bridge where the basement wall meets the soleplate as its outside the warm envelope. I found ICF more expensive over all as the SIPs roof added a lot of cost (could go timber and self insulate I suppose) plus the construction of floors, walls etc. The attractiveness of timber frame, and MBC in particular, was the completeness of the quote (you get a lot for your money, you can pretty much move straight to first fix once your windows are in and roof on) and the speed of onsite build. I did look at Thermohouse which is an ICF product with a structural floor and roof element. Link to comment Share on other sites More sharing options...
LadyBuilder Posted December 12, 2017 Author Share Posted December 12, 2017 (edited) 42 minutes ago, Oz07 said: If going for mbc style twin wall wouldn't it be far more sensible to have external insulation on basement? Aren't you just introducing a cold bridge and/or painful detail otherwise? I just figured what the question was... My basement is a lot bigger than the house on top, have a look at the plans. So I'd never be able to prevent cold bridging that well, or at least I haven't figured out how to yet Proposed house levels.pdf Edited December 12, 2017 by LadyBuilder Link to comment Share on other sites More sharing options...
caliwag Posted December 13, 2017 Share Posted December 13, 2017 If you are considering twin wall, consider Solotimberframe who have experience of twin wall. They appear to have a good reputation...standard internal designs and bespoke. Steamy tea, I'm a bit unsure how our 'small house' ideas differ. Link to comment Share on other sites More sharing options...
Oz07 Posted December 13, 2017 Share Posted December 13, 2017 12 hours ago, LadyBuilder said: I just figured what the question was... My basement is a lot bigger than the house on top, have a look at the plans. So I'd never be able to prevent cold bridging that well, or at least I haven't figured out how to yet Proposed house levels.pdf I see, sure someone here will be able to come up with a solution! Link to comment Share on other sites More sharing options...
Bitpipe Posted December 13, 2017 Share Posted December 13, 2017 13 hours ago, LadyBuilder said: I just figured what the question was... My basement is a lot bigger than the house on top, have a look at the plans. So I'd never be able to prevent cold bridging that well, or at least I haven't figured out how to yet Proposed house levels.pdf Quite impressive You could potentially wrap the whole basement perimeter in EPS 200/250/300 depending on loading spec. You would lay it first directly on the ground (on some blinding), lay your steel on that and and build your slab off it. In doing this you can copy the MBC method of attaching the UFH pipes directly to the steel and save on screed and additional insulation & labour. It will be a very low temp (35o) system with slow response but will keep you warm underfoot especially if you tile the floor Then Fix EPS against the steel piles (low expansion foam would be enough to old them in place and fill gaps) and then build your steel against it and effectively using the EPS is as one side of your shuttering (or do the walls with ICF). Build the lid with RC as normal and clad the top with EPS before backfilling - effectively you strive to wrap the whole basement in insulation from the outside. You can then run this EPS up to the perimeter of your house walls. Laying EPS in this way is not a skilled job, I should know as I did all of ours . Note I did not use custom made EPS (i.e. the Kore system that MBC use) just bog standard 2.4m x 1.2m blocks in 200 and 300mm thickness. It can be cut easily with a chainsaw and the heavier stuff does not go anywhere when positioned. You can also use small lengths of rebar as pins or bent into staples to hold it in place. This is contingent on using WPC but I really suggest doing a full cost breakdown of the two systems as there is a lot of additional cost with internal membrane, its labour intensive and the detailing is critical. Plus you have the ongoing maintenance of pump systems etc, contingency for power outages etc. Finishing our basement internally was very cheap - a bit of latex to level the floor (could have power-floated to avoid that) and dot & dab plasterboard on the walls with services behind (D&D gives you 30-40mm to play with). Inherently airtight too so. Look at https://www.mea-group.com/de/ for their range of lightwells and basement windows etc. We used three of their largest GRP lightwells and they were very easy to install. If you need sumps & pumps to deal with those, at least they are external to your waterproof envelope. If you use SIPs or another TF system, your soleplate would be sitting on the slab (basement lid) but inside the EPS envelope - protecting you from cold bridging at the sole plate and the associated issues. Or build the walls from ICF and continue the insulated layer vertically with that. You can use suspended concrete floors with ICF or cast in (or retro fix) support for a timber floor. Link to comment Share on other sites More sharing options...
SteamyTea Posted December 14, 2017 Share Posted December 14, 2017 23 hours ago, caliwag said: Steamy tea, I'm a bit unsure how our 'small house' ideas differ. By about 50m2. Just teasing really Link to comment Share on other sites More sharing options...
caliwag Posted December 14, 2017 Share Posted December 14, 2017 Aye, of course, there's many ways to skin a cat (referring to catfish, so as not to offend!) Cheers. Link to comment Share on other sites More sharing options...
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