MarkyP

I saw a new build estate locally under construction with PIR cavity walls and stopped for a look, the insulation was ill fitted, gaps everywhere. I think its a case of out of sight, out of mind on such builds. But the thermal bypass must be tremendous. This insulation will be coupled with aerated block work to the inner leaf which will crack behind the dot and dabbed plasterboard = a nice steady breeze blowing through the plugs and under the skirting from the outside. Far, far better to go fully filled with a decent thickness of mineral wool. Makes it harder to leave gaps. We had some rubbish, really sloppy brickies on our blockwork extension but I'd gone for a wide fully filled cavity on the extension, even these were able to keep the insulation batts tightly fitted without too much mental strain, albeit with me checking it constantly.

will the new weep holes do anything? I've often seen these on retaining walls and wonder whether they really serve any purpose. I would think they might perhaps in conjunction with a french drain, or some other means to create a space for liquid water to pool.

I think the primer is to control suction in the subfloor, stabilise dusty surfaces and promote bond between the smoothing compound and the subfloor. It's used neat on non-absorbent subfloors, and dilute on absorbent surfaces. I think the can of primer is about a tenner, cheap enough that I'd never considered not using it.

setcrete is really good quality stuff. It's actually a re-badged FBall product . The deep base is good, I used some just last week but it does have a grittier grain size and can be a bit harder to feather out thin. I would only use it for a deeper application. For 10mm or so, I would use the setcrete high performance levelling compound. This is good up to 15mm in a single application, is much less gritty and in my experience does flow and level slightly better. My theory is the deep base has a slightly gluey nature which is necessary to hold the aggreagete in suspension in a deeper fill. With setcrete you'll need to prime rather than wet the subfloor, read the prep guidance. Use the Fball/setcrete primer, it's green stuff, acrylic based. Adding a little extra water does help it flow but from memory it's recommend to use about 3.5l per bag, and I've added an extra 250mm to 350mm or so. Too much extra water and the suspension of the fine aggregates can be affected. I've used a fair bit of this over the years, just remember these are smoothing compounds which have self levelling properties to varying degrees, they don't self level all on their own! They all need a degree of trowelling out and careful pouring. A spiked roller brings it up to a lovely, pin hole free finish and removes trowel lines, but overkill for a one off job. one last tip - you can stick some window packers of appropriate size across the floor to guide your levels as your pour.

I'm no expert on approaches to flood mitigation but thinking out loud I could see tea cosy approach being preferred over cavity. I think you would certainly want to avoid mineral wool in the cavity if there was a risk the cavity could be breached during a flood. The stuff takes an age to dry out once wetted (experience of dritherm32 batts left in the rain on my site) and when saturated tends to slump and deform. If going with EWI, then I would think an open cell insulation would be much preferred. EPS is open cell somewhat vapour open so in a flood the wall inside if wetted would be able to dry outward. Closed cell such as PIR or XPS I think would not allow this, you'd need to dry from the inside only. I think there are few system suppliers who specify closed cell EWI in any case. There were issues a while back with PIR boards used for EWI deforming once fixed, "pillowing" I think was the term used. Nearly all systems I considered were graphite enhanced EPS. There are some that offer wood fibre or mineral wool options but neither would be suitable where there was a risk of water immersion. I learned that EWI grade EPS differs from standard stuff. EWI grade it is cut from aged EPS blocks which are dimensionally stable. Standard EPS is not and there is a theoretical risk the boards could deform causing cracks.

I think Tony's house (if we're talking about the same one!) is fully fulled wide cavity, similar to the Denby Dale passive houses. cavity walls as built new I think is still very much a standard and I think low risk in terms of later problems, the claims you mention will be for retrofit cavity wall insulation and damp issues (it's a complex topic) but this isn't something that put me off a wide fully filled cavity in my extension. Cavity walls aren't as popular with self builders, particularly passive houses. However it can be done well. solid wall is an option I considered. Mortgage-ability is a factor, you may need an eye on a future sale and there can be a bit of "computer say no" from lenders against single skin walls. Admittedly this probably isn't aimed at well built new houses with wide format blockwork, rather at single skin brick walls built last century which lenders consider structurally unsound. However, it may be worth exploring to check you wont get caught up in the same bucket. Wide format blocks and EWI would be my preferred approach for single skin. EWI can be employed achieving what is called the "full tea cosy" method - a continuous insulation layer from footing all over the house, including roof (using warm roof approach). You can completely eliminate structural cold bridging. EWI can be rendered, timber clad (or any cladding - zinc, through coloured cement panels, etc) or even faced with brick slips (these are effectively slithers of brick applied like tiles with a mortar applied rather like grout). I have seen some high spec examples that looked incredible and you would never have guessed they weren't brick walls. IWI is a bit of a headache with condensation risk behind the insulation, and the issue of creating cold bridges with internal structural timber piercing through the insulation layer to the outer structural wall. It's typically a retrofit approach, not sure I've ever seen it employed new build.

by the way, EWI can seem a bit daunting but is in my view a superior approach where it is feasible. I have 100mm of graphite EPS EWI with a render finish and it has made a huge difference. It is a bit of a project though and cant' be done a room at a time like IWI so I can understand you being put off. There are sometimes external detailing headaches as well so it's not always ideal. And there may be conservation reasons which rule it out. But, these issues aside, it does remove all the condensation and cold bridge headaches. There are now lime render products for EWI for heritage applications as an existing rendered period house would look wrong with a modern render such moncouche or thin coat over EWI. But you can float finish pre-coloured lime over EWI or apply a mineral paint over a lime base, both look lovely.

I can't find a citation but recall reading about the use of breathable systems to mitigate the risk of interstitial condensation. If I recall correctly a higher (i.e. less insulating) u-value was designed (and accepted by BC) such that sufficient heat would move into the uninsulated wall to reduce or prevent formation of condensation in any void between the insulation and the old internal wall. I guess this would drive the dew point further out into inte fabric of the solid wall where it would form and evaporate harmlessly (assuming outward vapour open wall build up to allow diurnal/seasonal flux). The system here was wood fibre and lime plaster, vapour open, no VCL. Another approach would be to use an insulating plaster. There are various products on the market using cork, perlite and other additives typically to a lime based plaster. These are not such good insulators so a much greater thicknesses is required to achieve a given u-value. However, the nice thing here is there is no interstitial void so any condensation that forms would do so in the outer fabric of the wall. It might be that cost, the removed condensation risk, and desire to not lose too much internal space, would mean BC might accept an improved u-value that didn't meet the normal target. just as an example, the manufacturer of Bauwer light claims a u-value of 0.5 when applied @ 80mm over a 600mm solid stone wall. in these examples the u-value was traded off against mitigation of condensation in the interstitial void in the void by heat transfer or removing the void entirely. In either case, a u value of 0.5 I think would make for a dramatic improvement over a solid stone wall.

I had looked at this, I guess the joist strips with floating timber deck is a cheap version of the same. I was thinking of getting the impact noise benefit without the cost and hassle of the full system. It's temporary storage of building materials, will be an occupied upper floor when done.

I thought upstairs was going to be carpeted, but seems the Mrs thought wood, hence my worry about impact noise. regupol looks interesting, seems you can bond that to the chipboard, and then bond an engineered floor over that.

I'm almost ready to lay a chipboard floor in my loft conversion. I've been thinking about the issue of sound transmission. I've tightly placed 150mm of rockwool RWA45 between the (220mm) joists which is already far more sound insulation than any other house I've ever owned but I'm having one last look at options before I put the chipboard down. (The option of adding resilient bars and double layer of PB below just would have been too disruptive, it's a large bungalow and would have been 5 rooms' worth of ceilings to take down and replace. however, I recently saw a system which uses a dense foam strip over the top of each joist, and then the chipboard laid atop this but floating rather than nail or screw fixed. I'm assuming this is helpful in reducing impact noise through the joist structure. Does anyone have any experience with this solution? I have loose laid some of the chipboard floor to create a temporary storage deck and it sits nicely on the joists with no bounce or rocking so wondering if actually it might be easy enough to float the 22mm deck, gluing the T&G sheets but not screwing into the joists, leaving this 10mm dense foam pad to absorb some impact noise. The joists are at 600 centres so one concern is that heavy furniture in one area might cause some flex in the chipboard between joists, lifting it elsewhere due to the absence of screws.

Our block layers hated thermalites and were much happier when I specified medium density. Thermalites are much more prone to cracking than medium density, especially around openings and reveals. And they are ridiculously absorbent and I think this makes them hard to lay, within a few minutes of laying a mortar bed along a course it's started to stiffen before you've had a chance to lay the blocks on top. You have to pirme the edges of the blocks with water as you go to try and control the suction. And in warm weather the water can be pulled out of the mortar bed very rapidly, before it's had time to cure properly. Also, they are a beast to wet plaster, requiring copious priming with PVA to kill the suction. As above, medium density are going to create a better sound barrier and are much nicer to fix to. The only one who grumbles about medium density is the poor labourer who has to haul them up the scaffold all day! I'd use them everywhere, a small increment to insulation layer will offset any lost thermal performance.

and the other question is whether you should be paying for it at all if the builder has quoted for the work and is working to a set of detailed design drawings. The question I guess is why this add on has become necessary.

assuming there aren't hidden complexities here (and that this per an engineer's design) I would get a quote for supply of the steel plate - try a local fabricator or two and also a regional stockholder ( I used Parkers and they were cheap and price was very negotiable). Then get a hourly rate for site work from a local welder, and an estimate of the hours. Then you can have a chat with you builder and ask if he's mistakenly added a "1" in front of the price ?

typical build up would be hardcore, 25mm sand blinding layer (to protect DPM from being punctured when concrete is poured), DPM/Radon barrier, concrete slab, insulation, polythene separating layer (500 gauge poly), UFH pipe worked clipped, screed. the polythene separating layer over the insulation isn't really as a DPM, it typically serves to protect the insulation from contact with the wet screed. I believe this is because the foil facing of PIR reacts with wet cement. It is also, where a liquid pumped screed is used, to create a bath to hold the screed and stop it running down the sides or between the insulation sheets before it sets. Some have used a further DPM over the slab where there is concern it hasn't dried fully.

is it too late to consider wet plastering? It's a parge and finish in one. Also even well pointed blockwork is still going to have hairline gaps in places in the joints. If you have to dot and dab I would use a parge coat. Prime the blockwork with PVA solution first, it's a nightmare trying to soak thermalites as they will take an amazing amount of water. Sand and cement wet slurry with fibres or even a thin skim of bonding or hardwall would do as a parge I think. But even with a parge, if (when) the blockwork cracks then you'll get a potential air leak behind the boards. with wet plaster, any cracks that do appear can be seen and addressed. You'll never know what's going on behind the dabbed boards.

yes this why I said I will need to double check choice of tape. If the tape isn't sufficiently vapour open then this would indeed will be a waste of time. My aim is to improve the vapour permeability of the OSB with a series of air tight but vapour open holes.

personally I wouldn't but there's more than one way to skin this cat. The tape will adhere to plaster in my experience. But you will have to skim over the tape, and then feather out into the body of the existing plaster which some might find a fiddle as you have to cover the tape suffuciently to avoid it grinning through. this is why dry lining boards have tapered edges, to ensure the tape sits below the finished surface. If you chip back the existing plaster you can tape in the recess and then fill flush to the old plaster. Chipping back cleanly can be fiddly. And you will still have a joint between the old skim and filler. This wont be as crack prone but still might hairline crack with doors opening and closing. edit to add that the latter will be easier to get a clean finish if you haven't done much of this sort of thing before.

I have OSB 3 sarking, as designed the intent was to full fill with mineral wool between 170mm deep rafters and then 70mm PIR below. This was passed at bc subsmission stage but since on site BCO has questioned condensation risk on the inside of the OSB. A VCL would if perfectly fitted address this from a CRA point of view but there is a tricky detail at eaves (this section is of the building is retrofit) and around dwarf wall uprights in the trusses which will be a fiddle to detail the VCL perfectly so perhaps not unreasonable of BCO to question whether I will 100% prevent vapour (or even air) moving from warm side into the build up. So my plan, while it will be a chore, is to drill two rows of 8mm holes @ 200mm centres through the OSB in each rafter bay and then run a strip of air tightness tape over each row to prevent wind washing of my insulation once fitted as the OSB was all carefully taped to be wind tight. Above the OSB is a ventilated counter batten void, breather, then batten/slate. I need to double check the tape of choice to ensure sufficiently vapour permeable. Have yet to discuss with BC but think this will address concerns.

if you are patching over an underlying joint between your new plasteboard and the existing skimmed walls (which it sounds like you are) then I would use plastering scrim tape over the joint before filling. Plasterboard jointing compound (used to fill joints in dry lining) is relatively forgiving stuff to use and is very easy to sand. You'll need a couple of coats, first one to get a skim over the tape, and a second to feather in, then a light sand to smooth any blemishes. You can get tubs of ready mixed jointing compound from most builders merchants and more trade focused sheds. I find it easier to prime existing plaster (unless already painted) with weak PVA solution first (leave to dry) as the joint compound stays live longer and is easier to feather out with a trowel. if you need to finish sand use very fine grade paper or you will get visible swirls when you paint. don't confuse with ready mix patching plaster products. This stuff is often grey colour and is handy for some jobs but is hard to sand, often dries a bit harder than the original skim so you can struggle to sand back and get a clean joint.

I've got a bosch blue sliding mitre saw. From memory about 350 quid new. It's great and as others have said, you find all sorts of uses. For stud work I used a cordless skill saw in the main for reasons of speed but for anything requiring a precision cut, or lots of angle cuts, then mitre saw really comes into its own. I used mine yesterday to create a precision perfect mitre joint in 2.6m long window board which was made from two pieces of MDF, it's painted and you have to look really, really hard to see the joint, would have been impossible without the mitre. Architrave and skirting is made so much easier with a mitre saw, as well. I bought a quality saw expecting that I'd sell it on after the build but actually we're now planning a DIY built timber framed outbuilding, and even after than I just expect I'll keep it because it's so handy and makes such good cuts. I'd say get yourself one, there's nothing like a shiny new tool to lift your spirits on a cold winter's morning. ?

I noticed you didn't get a response so thought I'd share some thoughts.. what is the sarking made of? If it's lengths of timber with small gaps between each strip then there ought not to be a need to ventilate as it will be vapour open (with your breather and slates above) so the condensation risk on the underside of the sarking would be low, or any that did form could evaporate away readily when conditions suited. If the sarking is sheet material, like ply or OSB, then this is less breathable and the standard approach would be a ventilated void to mitigate perceived risk of condensation forming on the underside of the sarking. However, there are multiple examples of builds which have eschewed this common thinking and fully filled under OSB sarking ( using spray foam, blown cellulose or mineral wool) with vapour control to the warm side. In your case, I don't understand what the 10mm void is doing. Perhaps PIR boards are easier to source in 150mm rather than 160mm? Or perhaps this is just a fitting allowance - you mention an old house, are the rafter voids all universally 160mm deep? Again, if the sarking is strips of wood with lots of nice breather gaps, then I don't think the void is an issue. You could use a warm side VCL as an additional measure for peace of mind (just taping the foil face PIR under rafter would do, I think) I can't comment on the questions about the differences between the sheet in insulation types.

I've found a small dealer locally with 3 x 2.5t kubota machines. KX61-3 and UR25-3. These seem pretty well regarded so going to go and have a look. Also, by bizarre coincidence, a bloke knocked on the door recently who it turns out grew up in our place (well, in the timber shed we demolished). He was passing and just wanted to have a look around. It was then 50 years back a full blown small holding and was very interesting to learn about the history of the plot. And it turns out he's a semi-retired machine operator and he gave me a load of contacts including a local plant engineer who will for a small fee come and inspect any machine I am thinking of buying, which was nice.

could make a nice feature, a walk on glass floor in the kitchen with flowing stream running underneath, perhaps some mood lighting and the odd trout nipping about.

crikey, what a job. Epic is an understatement! 16 hours a day for 19 days straight, I think that surely must be some sort of build hub record. I've done some big DIY stints on my project but nothing to match that. I guess it's one bit of your project you'll never forget. Well done. I hope you'll forgive me for saying, I do wonder if you might be slightly insane (just very slightly) ? what do you plan to lay as a finished floor covering? It's almost a shame to cover something up that was such a labour of love. Could a lime screed be polished and sealed?