Visti

How thick of a screed layer did you install to fit the UFH? We've planned for 75mm but have been warned that this may be insufficient by MBC. So are considering an increase to 100mm. Current composition (above EPS) is: up to 24mm reinforcing mesh (2x12mm diameter steel) 16mm UFH piping 35mm concrete cover Key question is whether the 35mm is enough? and what margins of error should we accept? ~/-5mm?

Our reality check that stopped WIBNIs was going to a quantity surveyor. It cost us more that I'd like, and I wasn't happy with the job they did, but it helped translate all these decisions we were making into actual £££. With that, nearly all the luxuries went out the window and we've been very cautious on scope creep and new ideas unless they bring genuine benefit or we feel make sense as a long term investment. EDIT: also a good one we use is SEP (Somebody Else's Problem). If we're putting it in to make it more marketable at the end of our stay (which hopefully will be a long long time) then it is most certainly not our problem today!

I did not know that about a Larson Truss... I suspect it's because we just weren't aware of the loading (yet to engage on engineering, but we're kicking off promptly). More insulation is always a win, but the beads + cement board + brick slips appears to be a much more complicated setup (both in time and cost). I'll have to do some costings! Using solid EPS may make it more viable as a DIY method thinking about it. As for the ventilation of the void, I've done some digging in the Bregs and it's clear that it needs to be there. Reg c 4.19. The EPS beads may still be an option however, though I'm still awaiting our warranty provider for confirmation of acceptance of such a solution.

This is the spreadsheet in question: I'd suggest that you do the calculations for the entire house rather than per room as that can get quite complex, which is exactly what that model does. First you need to know the following for each of the external surfaces of your house (Foundation, Walls, Roof, Windows, Doors) Surface Area (m2) U-Value (U) Temperature difference (dT) - usually 21 degrees inside, minus the ave outside temp. This will change with the seasons mind! That loss in Watts is equal to m2 * U * dT You can convert that to kWh to identify the total cost of heating your home given your current £/kWh for electricity by your energy supplier.

^ This. I've not heard of any other self-build mortgage with this requirement. Not sure how anyone can reasonably expect people to live on their site when they already have a perfectly reasonable house/flat that they're already in...

That is the first time I've heard of that condition... why are they stipulating that?

Nonsense, looks great! People need to get used to a bit more variety in the buildings!

Schrodinger's Shower!

That £18m project was was rejected, but two other projects of his in Oxford were approved around the same time: article. A look at the google street view on those roads mentioned doesn't appear to show anything 'special' with regards to those house designs I believe the one riddled with issues was the Applewood Development in Stroud (Telegraph).

You can start by calculating the minimum requirements based on your # of rooms using the Building Regs part F. You can see my own calcs doing just so here: As you can see from the quotes we got back, the unit spec and cost varied quite a bit for the same plans... it then becomes more of a factor of what package you'd prefer.

The principle concern with ventilating the void beneath the beam and block appears to be the prevention of gasses accumulating rather than damp. Even though the likelyhood of gasses accumulating is remote, it's not something I think we can rule out 100%. Filling the void with EPS of some sort would solve this, but in the shrinkage scenario a void would be created anyway... not quite sure how to address that particular issue! I'll be raising it with out warranty provider to get an early steer, but it's the BC that ultimately makes the call.

Noted! hadn't thought about that!

Perhaps modifying a grinder with some flanges to act as guides and a thick disk of some sort? It's take some tooling and the trailing of the right sort of disk but doable I'd think. Wouldn't double plasterboard, outer to the floor and the inner raised just slightly to create the gap be viable?

Now that isn't a half bad idea folks! There is even compressable EPS insulation that is specifically designed to deal with clay heave. A 100mm of that beneath the slab rather than an extra 50-100mm above ought to fill the air void whilst giving the added U value performance! Ideas ideas! I'll have to check out the fact about the ventilation requirement in both cases. Looks like some bed time reading of the building regs. The roof design has no overhang. There's a hidden gutter behind the cladding, but that's it. Any reason why it's be more of an issue there than terminating further up?

There is with their tapered edge boards, though we were planning on using the square edge boards as it is more DIY friendly... we may however have to reevaluate that given the desire for shadowgaps!

An update for you all following your suggestions! Use of periscope ventilators will maintain a FFL level with the external ground level, 4 in total. XPS cavity insulation extended down to the base of the cavity, which will lengthen the thermal path through the inner leaf block as suggested by @bissoejosh The foamglass course has been removed, replaced with 50mm of EPS services zone insulation between the inner block leaf and the screed/slab. The thermal bridge therefore from the underside of the Beam & Block, up the block inner leaf, and though the 50mm services zone insulation has a U value of 0.28 W/m2k. I'll have to ask what the equivalent was with the foamglass! The current U value of the floor is 0.15 W/m2k with 200mm EPS, which we're looking to increase to 250mm (~0.12 W/m2k) or perhaps even 300mm (~0.10 W/m2k) given @JSHarris points regarding the larger delta T with air vs soil in winter. Given the walls are MBC's 300mm cellulose @ 0.12 W/m2k it'd be foolish in my opinion to leave it at 200mm of EPS.

Any idea if there's a similar solution that doesn't involve a skim finish to integrate these skims? We're heavily considering Fermacell and were hoping to do away with both skimming and skirting boards, but simply leaving a gap between the board and the floor wont cut it as @Stones has already pointed out. These appear to solve that problem but require skimming, which would negate one of our prime reasons for using fermacell in the first place.

Do they blow too however?

Awesome, that just saved me £40 on several books I'd been planning on buying for a while! (Building Services Handbook, Building Construction Handbook and Architects Handbook fyi)

What worked Reserved our desired plot in Oxfordshire following many years of searching and waiting for Graven Hill Found ourselves a great architect that has designed us an excellent house and have helped us immeasurably. Signing up to this forum and getting some stunning advice. Most notably on our costing estimates. What didn't work Price of our plot was ~£30k above our expectations, cleaning out out original contingency before we even began. Spent £780 on a Quantity Surveyor which could have done better by ourselves using SPONS (lesson learnt!) The planned budget for the house build has had to be increased by about 20% overall due to material price rises following the Brexit vote. Submission for PP didn't get through before the end of the year as planned, pushing out build out by at least an extra month.

If I'm not mistaken it's this Genvex 3 unit (or similar) from Sundhus.dk, isn't it? Fyi; if anyone needs clarification or help with Danish even with Google translate and their excellent English, feel free to reach out to me. Being a dual citizen has its benefits!

I take it that is the 300mm cellulose insulation? Or did you add additional layers in the end? I'm finding it difficult o justify double the price vs a Renovent Excellence 400; does the heat pump make such a difference?

The ventilation is not an aspect I'd considered to date, and I'd not be adverse to raising the FFL either. I'll make a point of addressing this at our next meeting. Thank s for pointing it out! I am completely with you there and am very aware that the thermal performance will be lower given the typically higher delta T of the air vs the ground. The dynamic nature of the temperature will also be more noticeable internally and more difficult to compensate for in the UFH. Unfortunately our choice at this point is to either to proceed with a B&B or find another build site not associated with Graven Hill! We'll probably be increasing the depth of the EPS from 150mm to 200 or 300mm to combat this! I like the idea of carrying the cavity insulation down and getting rid of the foamglass... I'm well aware of the price, hence why you can see there's only one course so far! I'm sure we can get the depth needed. Sounds crazy, but I like the way you're thinking. Some calculations over the holiday may be in order.

I believe there is technically, but it's not a course we're willing to pursue further as we've already challenged the authorities (Graven Hill) and the Structural Warranty provider (Premier Gaurentee) several times and gotten nowhere. It got to the point where they'd just reference the plot passport (similar to T&Cs) which explicitly states a requirement for a suspended slab. So better to save our energy for the next encounter!

We're finally at the point were we've reached one of my most concerning details of our build (so far): the footing between the timber frame and the foundations! As some of you know, we're going for an MBC frame but are unable to make use of their slab due to the clay on our slot mandating a suspended foundation! Hence we're going for a beam and block setup, but have been concerned regarding thermal bridging. This is what our architect has suggested, and I'm curious as to what you all think! You can see that our 300mm wide twin-stud TF (cellulose insulation) will rest at least 150mm above ground level on brick externally and low density block internally. Key component will a single course of foamglass blocks (such as Marmox Thermoblock, Purenit or Compacfoam) to reduce the thermal bridging. We’ll also add in XPS insulation between the structural supports and also a small amount of insulation (undecided what type, rockwool?) overlapping the TF and structural blocks along the inner wall. About 200mm of EPS insulation will go down on-top of the beam-and-block foundation with a 100mm screed floor on top of that. I've seen similar alternatives suggested, such as Touchwood Homes method that @bissoejosh suggested and others in the thread below which appear simpler than the above. Are we over-doing it potentially?