WWilts

Strong theme here. PM quote was from someone far away, who would not actually hire trades. Merely advise. So they would be of little use in terms of locating tradespeople. For that route would need to get to watertight stage, and then hire trades as and when available to finish the inside. Food for thought. Nobody yet mentioned construction risk. Defects. Is that a concern when trades are hired direct, each trade blaming the other for defects? Main contractor can be pinned down but not individual trades. Or is that a trivial risk? Many have hired trades direct.

Trades direct or Main Contractor for the build? Context: traditional block & brick cavity wall construction. 200sqm over 2 floors. Not in a position for DIY. Once shell up feel more confident of hiring in trades for internal works / further ground works, landscaping etc. Trades direct or Main Contractor - Which would you choose and why? Project Manager consultant available, fee roughly 7% of predicted build cost OR £90ph. Will also provide their (presumably favourable) trade terms for any trade accounts we set up with builders' merchants. But made it clear that construction risks would remain with us, not with the PM nor the trades. Main contractors / builders - a few interested and available within a reasonable time frame. Some open to agreed target cost with gain share. Some open to contracting one stage at a time (weathertight shell -> internal works -> additional groundworks & landscaping). Trying to decide. What would you do and why?

Thanks. Great tips

Tks. Is that the same as Joist Hangers? Still trying to learn the terms. Plumbing is main worry. "Fully filled back in". Does that mean plastering to fill in gaps that remain? Apologies for being so ignorant about the terms used.

Alternative approach instead of airtight membrane: Internal airtight layer - Plasterboard with tape to seal joins. Plasterboard is in the equation already Has anyone found plasterboard + tape ok for airtightness?

Any serious disadvantages to this option for running services in wall? https://youtu.be/jd84Mtt8IlA

This seems like a way to include internal insulation too. Improving the walls U value. How do folks with internal insulation run services through the void? Would fixing battens over the airtight membrane involve creating airleaks in the membrane?

Airtightness required 4.0 Not against doing better, of course. But cost control is a priority. Two storey. Block inner leaf of cavity wall. Initial design is plasterboard on dabs. What materials would you advise to maintain airtightness? Damp-proof membrane seems the front runner. But where exactly in the wall layers? Or what else that is reasonably priced? How would you run services so that it all looked neat? What approach would you take to allow attachment of reasonably heavy stuff to walls in future?

Don't see much mention of fire risk from EPS beads in cavity walls. Presumably because the risk is negligible. But Dritherm 32 has zero fire risk. Is that sufficient reason to choose Dritherm over blown EPS beads? Given the often poor workmanship in installing Dritherm or similar?

My guess is wall figure

Question: Can Dritherm mineral wool slabs be used with block inner and outer leaves, if thin joint blockwork is used? Any serious potential downsides? Any more economical / buildable way of cavity wall insulation if thin joint blockwork used for inner & outer leaves? Thanks Context: Need to control costs, for better or worse. Not forever home. Non-masonry options ruled out for various reasons. Site foreman, scaffolding costs etc all increase with duration of build/delays. So, for better or worse, duration of build is important consideration. SAP pass with wall U value 0.25, airtightness 4.0, floor over slab insulation 100 mm Celotex

Great tips, all. Biggest fear is that a potentially £1500/sqm (or less) build might turn into a 2500+/sqm build. If costs creep. Especially since time not available for DIY. (nor skills) Tempted to try target price contract with pain/gain shared with main contractor if they bring it in above or under the cost target. If they accept such a deal.

No. Can fake it, but honestly no. And still trying to get my head round the tradeoffs between build methods/ duration & associated overheads at site.

This is a real fear. There is no limit to overspend for a newbie. Safeguards seem to include: More or less guaranteed maximum price from a builder/main contractor who seems trustworthy, (even if price is inflated a bit)? OR Pay a project manager/QS who is likely to understand and implement the cost control angle? Or other approaches?

What are your top tips for keeping build costs down? (apart from doing project management, or not building at all)

Very helpul, thanks

Very helpful. Thanks

Main incentive is short time to weathertight. Then it's less daunting to self-manage this alongside many other commitments. Plus outer leaf blocks can boost the energy efficiency of the wall relative to brick or stone, I believe. Is that mistaken?

Yes, basic cavity wall was the original design. Failed SAP. Interested in improving energy efficiency in reasonably cost-effective ways, anyhow. For SAP and otherwise too.

True. Looking into it.

Underfloor heating upstairs?

We're out of our depth on this. But we're in favour of boosting SAP scores. Just don't want to go silly with the spend.

Thanks

Somewhere between, because of 5 yr horizon. Minimise costs of build + 5yr running, while still making it attractive to the next occupants.

That's an angle not considered before. Quickly reaching weathertight stage was incentive for thin joint blockwork. Perhaps it's a bad idea?