WWilts

Builders are pricing to specs. On the whole, a modest mid-spec house. Nothing astonishing. 4 bedrooms, 2 storeys. 200 sqm. What data cables are recommended, for reasonable performance options and some future-proofing (without disproportionate boost in cost)? Currently specs include only TV cable in every room. Thanks. (PS Non-techie here, so translation to simple English always gratefully received).

Great tip, thanks

A way of life, it seems, once hooked

Thanks for the heads up!

How so?

We'll fail SAP with 5.0, so they won't convince us

Getting the plasterboard junctions well taped seems to be the critical point, as well as sealing windows/doors. Will aim for as low as possible, then might well achieve better than 4.0

Neat way of looking at it. Had not occurred to me. Main contractor/builder who project manages trades, supervises & maintains standards, & is happy to accept an independent estimate of quantities. They normally buy plots & build to sell off plan. Probably going through a lull at the moment, so available for this. I offered them a share in cost savings too. Already they proposed some ways of saving costs.

Yes, and if we aim for 4.0 we're bound to get 6.0. So aiming lower is a good idea

That's my hunch. Airtightness 4.0 preliminary test at watertight stage is main safeguard. If they get that, SAP pass assured. Architect will supervise & give CML certificate.

Yes, D likely to be hands-on. Might even take on the site foreman role. Price from A awaited

Yes, no double counting. The spreadsheet allows profit/overheads/contingencies to be set to zero if desired.

A few builders interested, each suggesting a different approach to the contract. A. Main contractor fixed price B. Main contractor till water-tight shell, with airtightness preliminary test. Then individual trades for the rest, or main contractor hired for the rest C. Labour only guaranteed maximum price including profit till water-tight shell with preliminary airtightness tested, materials purchased by us using trade account set up by builder in our name (hopefully with their discounts applying to us). Others contracted to supply and fit the rest D. Main contractor agreeing to use Estimators Online quantities & prices, 10% profit, 5% overheads, 5% builder contingencies E. Main contractor with target cost, guaranteed minimum profit for them, plus incentive payable if target cost met, plus half share in any cost savings All seem reasonably reputable. Option D does not have regular staff or regular subbies. Others do. Context: No time or skills for DIY. Which of the approaches would you choose, and why?

Aglite has relatively high thermal conductivity compared to Durox Supabloc. (see attachment) So 100mm cavity filled with k=0.032 Dritherm32 or enhanced grey EPS beads + Aglite 7N inner leaf will fall short of U value 0.25 Either Durox Supabloc (k=0.17) or slight increase in cavity width required to get the wall U value to 0.25 Full fill PIR boards (Mannok Isoshield) tongue & groove, pricey. 97mm of that would easily take a 100mm cavity under U 0.25. But pricey Aglite cavity wall U value calculation.pdf

Tks, great info & helpful to see it laid out so clearly. Easy and cheap without increasing wall thickness is the goal. U value 0.25 acceptable for SAP. Celotex themselves clarified to me that their product requires an air gap of 50mm, or if building control accepts then 25mm. So, quite right Given external wall thickness out to in: 102mm brick + 100mm full fill cavity + 100mm block Cavity insulation either Dritherm32 or enhanced grey EPS beads blown in (k = 0.032). Leaning towards the beads because it's possibly more reliable for insulation. For inner leaf leaning towards Aglite Ultima 7N block All becoming frighteningly real now, because specs and quotes are being discussed with prospective main contractors.

Fixed price sort of puts an upper limit on how much you will pay out (apart from variations). Cost plus incentivises trades to maximise client's expenditure by going slow, buying conveniently rather than competitively, pushing for variations (some of which will be definite improvements that benefit the client). We're at a similar stage, seeking quotes from very detailed tender - drawings plus QS estimates (estimates available for £186 incl VAT from estimatorsonline.com). Let's see if the QS estimates encourage sensible quotes. Contractor just needs to decide their profit/overheads level, assuming their QS more or less agrees with ours. That's the theory, anyhow. Let's see how it pans out. Trying to get agreed target price with share in cost savings. And agreed day rates for unforeseen variations. Till watertight shell / first fix to allow airtightness 4.0 to be tested. Fallback option is architect-recommended builder. They have worked together before. Asking for similar quote from that builder too. Nice low price from architect for CML certificate and low hourly rate for additional work if needed. If all fails then invest in PM and hire in trades. OR bite the bullet and self-manage (despite little time or appetite for doing this). References also sought from builders. Interested to hear ideas on how folks are faring with various approaches to appointing main contractor or builder or trades.

Brick outer, 100mm cavity, block inner, plasterboard on dabs. U value 0.25 suffices Debating between Either Aglite or similar block 7N for inner leaf with enhanced EPS beads (0.032 lambda) blown in, or Concrete inner block 7N with Celotex 4000 90mm in 100mm cavity (0.022 lambda) Perhaps some other cost-effective option for 100mm cavity and inner wall?

U value max 0.25 suffices for external wall, block inner brick outer. Airtightness 4.0 suffices. Plasterboard on dabs internally. Cost control is important consideration. Likely to move from area in few years. Not against better thermal perfomance, of course, but with an eye on cost. What inner leaf would you use? Why? Can some blocks compromise a SAP pass even though the external wall meets the 0.25 U value? What insulation would you use and why?

Thanks!

Tks. "Heavies"? I should know exactly what that means, but I don't.

Noted.

Tks, good price even before bulk discount. £1.19/block. Strong too. But intrigued by your reluctance to enjoy the free beers. Would you be wary of aircrete 7N blocks too? And if so, why? (eg., Durox supabloc 7N or Celcon plus 7N)

Entrance porch is single storey. Cavity walls of porch continue up to first floor as external walls. (drawing attached, front/south at right). Outer leaf of cavity wall non-loadbearing. First floor external walls are, respectively 1) brick (side/west) 2) reconst. stone (front/south) Question: If brick and stone are not the preferred finish for the interior walls of the porch, what is the most cost-effective block that safely can sit beneath brick or reconst. stone? 3.6N aircrete? Other?

Now that's a thought

How so?