lizzieuk1

Have you also asked the water board? They may have minimum distance requirements along with max build over distances (I'd try to avoid that though!) We are having an insulated raft and have a min of 600mm hardcore beyond the footprint (with integral drainage) all round if that helps.

Well, that's created quite a stir with everyone eh!! I've taken on board all the comments, thankyou all for taking time to reply and share your views. Suffice to say we're investigating both options. The cost uplift of scc isn't that much, around 50%, so it appears comparable in price to having a standard concrete with a crew. I like the way the scc fully eliminates air pockets and fills around any rebar. Appreciate that we aren't experienced with concrete laying but, we have built 2 houses previously, alongside a contractor who did the foundations and shell (with us on site all day, everyday, OH is a stonemason so quite involved and I project managed the whole thing through planning to finance to internals and finishing - no small task but a very successful one) we've also completed a number of refurbs via our company so, not complete novices in the building arena - certainly not a concrete crew, but we are quite proficient in many areas! With an insulated raft it (base & insulation) will all be accurately levelled before the pour so, theoretically, the top of the raft should allow a perfectly level concrete finish. Feedback from the SE is that he doesn't like it for their rafts but, only because there is risk to the perimeter formwork (that doesn't exist with standard concrete) and risks of concrete getting under and lifting the eps - both these can be mitigated (with extra shuttering and a 2nd membrane) and there is no other structural reason not to use it. We will have ufh in the raft but that will be below the revar mesh so not a real risk of damage if a crew are wondering around with a poker. I think there has been a fair bit of 'fear factor' perhaps with lack of understanding about the product, but, that's not a reason for us not to use it. The Jury's still out on this one so we shall see.....

It's a mix that has added plasticiser, usually with a 10mm and below aggregate, it flows more freely than a standard mix into mesh etc and doesnt leave air pockets. It doesn't require vibrating or power floating as compacts itself to a fairly level finish. May need a bull float to get the final finish but nothing more.

I've asked the question of why, my initial thought is they're worried that the eps profiles might suffer damage from the pressure of a more liquid flow. We can mitigate with shuttering if that is the only reason. I can't find any other real reason why it wouldn't be suitable, seems it has the same inherent strength as standard mix. No fascination just a desirability to do as much of the build as we can and, this allows us to manage the pour etc, instead of needing a full crew to lay it.

Yes, we have a local company that can supply it and, its not much more than standard. A standard mix with crew comes in around £500 more, not much so we will use that if it is the best option.

I have asked if we can use scc and they have said no but, not given a reason. AFAIK the scc is made to the required strength(in our case C25/30) but has added platiciser to improve flow, I don't think it affects strength but, I'm certainly no expert, just reading up on the Internet concrete sites for info and so far that's what I've understood.

Does anyone know if there's any reason you can't use self compacting concrete in an insulated raft? (Not talking about flow screed types)

ooi are you doing the fan coil install yourself? Who did you get to design please? and which units?

Hi all, Having thought we had the best option for our roof sorted with an I joist design we're struggling to find a supplier who can design & supply the I joists. We have loft rooms so need open spans Has anyone got any suggestions/contacts who can help? Our SE has designed steel ridge beams to support the I beams but need a layout etc sorting. TIA

Sorry, i meant fan coil unit!

Tricky to decide the best solution. If we go Air con then a. The cost and b. We're only doing ufh on gf so then no option for supplemental heating on ff&sf. Yes, ashp but installed quote for (8) heat coils is 10k! If its that much we could get an mvhr heat/cool module and as installing the ducting anyway can upgrade to 100mm insulated ducts. But, is it as good as heat coils??? How easy are the heat coils to install? How do you account for them on the ashp sizing?? So many questions.....

Thanks JohnMo, all good info. Wonder if there's a way of dehumidifying along the route to help the cooling?

Yes, we are going to look at external blinds - still in early stage of costing these, but had experience of them at my parents place in France so know they work well. Good to hear the mvhr has helped - the Zehender comfoclime looks interesting as can actively cool or warm incoming air which could help fill the gap of wanting some comfort cool/heat on ff&sf rooms.

Thanks Mike, we're not too bad on the calcs for Overheating- just a small loft room that needs an extra 10L extract to pass. Roof will be blown cellulose & we've no huge areas of glazing. We will use the ufh on gf to cool but have 3 floors so wanting to get something on ff & sf if we can to offer a bit of extra heat/cool if needed - 8 heat coils installed coming in at 10k on first quote so feel there could he a better option!

I know previously it wasn't especially useful but wondering what the new offerings are like. The Titon Cool plus Q has a 3.3kW total cooling, or Zehnder ComfoClime which has 1.7kW cooling and 1.7kW heating. We were looking at heat coils for heat/cool on ff & sf (ufh on gf) but so far at 10k install that feels pretty steep! (Would be 8 coils to do so quite a few and not sure if we can do the install though still investigating that)