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Okay i'm exposing ignorance here so go easy on me. Also i only get about 25% of the technical language expressed in other threads!
Has anyone used hemcrete to insulate either face of solid brick walls, either by laying or casting on with shutters? Id love to talk to you.
As per my post in the newbies section - we're buying a brick solid wall terraced & end terrace house with lime horsehair original plaster throughout, and we want to insulate it. So we're looking at breathable stuffs to be compatible with our ecological ethos and the existing lime plaster.
Ive looked into several options - wood fibreboard, the Breathe hemp system, and hemcrete at 75mm thickness - the latter comes out cheapest. Our current agreed budget is 4000, we may have to eat into other budgets.
The property abutts the pavement at the front so we're thinking of insulating the internal face of these walls, and externally at the side and rear.
Does this sound right? I feel i need to know more about thermal bridging and interstitial condensation. Any links for these, or general comments or tips or recommendations? Specific questions below
Thanks Gem x
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Questions re. hemcrete:
Lime Technology company have told me that the wooden frame fixed to the wall that we will affix the temporary shuttering to will not take the NHL 2 lime plaster finish very well, so we may get vertical cracks in it. He suggested using an alkali resistant mesh in the base coat of our plaster finish - what is this, where do we buy it and would you recommend the same?
Because we're applying internally we are stuck for how to pour in the hemcrete when we approach the ceiling - we thought of casting a block separately to the correct measurements and then mortaring it in the final uppermost space between ceiling and the rest of the cast-in-situ hemcrete - will this work? Lime Tech also suggested potentially lifting the floorboards of the first floor to pour the hemcrete through into ground floor wall shutters - would you recommend this?
For the gaps in the floorboards on the ground floor, can we just fill these in with bits of board or cover up with hardboard, to prevent the hemcrete falling through into the cellar?
Can we cast hemcrete directly onto electrical wires, as we're having our rewiring done and there are drops on the walls we want to insulate internally?
On St Astier's website user guidelines for hemp construction, it suggests you can use a hemcrete mix like a plaster/render, by laying on instead of casting and shuttering. This would be easier for us, but when i spoke to Lime Tech they said the hemcrete wouldnt adhere to the wall if applied like this. Can you give me some assurance that it would work? The user guidelines on the website arent 100% clear to me either; would we apply a stipple coat of nhl5 etc first, and then the hemcrete mix? and after that, a nhl2 plaster mix to finish? Is there any more detailed set of instructions for using your batichanvre and hemp shiv for hemcrete please? Im going on Lime Tech's Installers Pack, to be found here: www.limetechnology.co.uk/downloads.htm Are these instructions compatible with St Astier products?
Can you tell me how an internal application of hemcrete as insulation interacts with a silicone injected DPC? which we have at the base brick level on our ground floor.
We hope to use hemcrete externally on 2 faces of our property. Unfortunately we have cement plaster and pvc paint internally on a kitchen extension; if we want to use hemcrete externally here is it totally incompatible? As in, would we have to remove the internal cement plaster etc, replace with lime?
On a similar note we dont know what kind of paint is on the external face of the walls we want to hemcrete internally - if its modern pvc paint i presume we'll have to strip it off?
The gable end of the property is on council land and a privately owned bus depot - we'd prefer not to tell the BCO of our plan to externally insulate this face but there are tree branches abutting our wall that we'll have to remove and we'll need scaffolding to apply, so....im wondering what peoples experience of doing work that will be within regs but not notifying the BCO is?
Hemcrete at 75mm will be nowhere near the Bldg Regs U value req't of 0.3W/m2K, (though it may help with 'moisture management' issues) but for 'historic bldgs' you may be able to negotiate out, but you will, almost certainly, require Bldg Regs approval, unless you are doing very very little bits. If the gable is visible I think doing it without B Regs approval is risky - and of course cannot be condoned by this Forum etc etc - BCO's do 'cruise' between jobs with an eye open for unauthorised work. Even if you comply, if you get found out you will be req'd to get a Regularisation Cert (125 or 133% of B Regs fee). I'd have thought the bigger issue relates to an arguable encroachment on others' land, both with the scaff and forever with the EWI. Party Wall act presumably also applies.
You specifically asked: ''....im wondering what peoples experience of doing work that will be within regs but not notifying the BCO is?''
The trouble is that, certainly at 75mm, your work would be nowhere near within regs. Let's say the BCO spots it, and you are automatically on the back foot. The *could* cut up rough and tell you either to remove or bump up till it complies. Human nature being what it is I would guess they could be less minded to negotiate on standards if you have already gone ahead and done it. I realsie you may not wish to involve them, but it may be best to ask. After all, you are publicising the co-op in the press, on a public forum and via your blog.
Good luck. Look for a Hemcrete thread by Jem Hayward on here. Stone bldg, and something like 250mm hemcrete.
Blindingly obvious, I know, but the less insulation the bigger the fuel bills.
It's not that hard to work out U-values for your current favourite options, then you can work out what thickness of material or combination of materials you will need to meet Building Regs. Then you can cost it again and choose. Loss of internal floorspace may be a factor for some of these options. There is not much point trying to "get away with" not meeting building regs on insulation - mainly because they are a minimum not a maximum. In the long run you will only wish you could have done more.
Perhaps you could get an easement or some kind of legal agreement to overhang the boundary with your EWI?
I believe expanded polystyrene is a bit breathable, you may find that the cost/benefit of this type of insulation stacks up, especially in relation to thickness(depth)
Re: Hemcrete, we used s/steel brick mesh stapled (s/steel) to the face of the battens so that we could lime plaster over it all. Worked well and easier to get hold of for us. Must not be galvanised though. Electrics can be covered with plastic plastering trunking stuff then you are away. Don't use galvy Elec boxes use plastic otherwise Hemcrete reacts with the galv and it goes rusty.
If you have the option, get the Hemcrete sprayed on, it takes forever by hand.
The top bit by the ceiling can be stuffed in by hand. When you mix it up you don't really 'pour' it in as it's more like soggy straw than runny plaster or mortar. If you want to know more get in touch.
+1 for getting your BCO onside early, you cross building control at your peril! But if you get a reasonable officer (they do exist!), and get him/her involved early they can actually be really helpful with stuff like this, they know the regs better than most after all.....
If you're tight for space you can always split your insulation external and internal, maybe the hemcrete as EWI (if you can do that?) and foam internally, or a layer of hemcrete both sides? Ideally you want the least breathable materials inside, with the vapour resistance decreasing as you go outwards.
The problem you might face is that eco insulation products tend to be very thick, so complying with regs and keeping it strictly green might involve a serious loss of space internally. I reckon for 0.3 you'd need more like 150mm of fibre insulation (between timbers) and about 175 of hemcrete (not between timber), versus maybe 50-60mm of phenolic foam for the same result. I have a similar issue (1700s 3ft solid stone walls, no chance of EWI) and much as i'd like to use wood fibre or similar, i'd have no house left :)
(declared interest/bias - i work for a foam/aerogel insulation supplier, however i'm certainly not knocking hemcrete and the like, it's a great product if you have the space)
I don't know if there is a BBA or similar cert (i.e. 3rd party certification of its - among other things - thermal performance) for Batichanvre, but there is some sort ofcert for 'Hemcrete'. If the product/method you use does not have 3rd pty cert, the BCO does not have to accept your 'alleged' U value assertion, and could discount it altogether. Same goes for using other insulants (e.g. 'Green' roof insulation) without 3rd pty cert.
I believe you can put the hemcrete over lectrical cables, though you will have to derate them (i.e. use larger cables than otherwise). Ask your electrician. You might also want to run them in conduit.
A chemical DPC is, to state the obvious, waterproof. So if you have insulation inboard of that, you'll need to make sure you allow some way for condensation to escape from the inside surface of the DPC. Perhaps drain down to some weep holes? Take expert advice.
Using breathable insulation outside an impermeable construction is not generally a problem. It's doing it the other way round that causes trouble. So your kitchen should be OK but yes, you may need to strip exterior paint on the front of the house.
What others have said about building regs for insulation and party walls.
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