Hastings

@saveasteading I am saving a Scottish stone farmhouse too. Deep retrofit rather than demolition, for sustainable reasons as well as heritage/feelgood reasons. Hardly changing the original layout at all. Airtight, breathable, MVHR design. Having added 100mm to the inside walls with the new internal timber frame I now have entirely got used to the reduced rooms size. To the extent that I am now adding an additional 50mm service void and insulation layer. In retrospect I wished the original TF design had been for even more insulation thickness. The building has been derelict for more than 10 years so qualifies as a new build for VAT reclaim purposes. A mixed blessing because newbuild status brings almost full building regulations with it, regs which often clash badly with old parts of the structure. In this case the only remaining parts are the old stone walls (everything wooden - stud walls, lath&plaster, windows, roof, floors, lintels - was removed) and their openings but they almost entirely dictate the design layout. If the property HAD been lived in less than 10 years ago I would have had many more options and a much easier ride. The main issues I wish I had known right at the outset: Digging out the ground floor in order to provide foundation for internal timber frame plus damp-proofing plus insulation is compromised by disturbing original stone walls which have no footings under them. 'Solved' by raising ground and mid floor levels a little, rounding the new slab edges a little away from the old walls and limiting insulation on top of new slab to 100mm PIR. Because the existing window openings can't practically be raised this makes all the windows a bit lower than is natural. The effect is slightly worse upstairs because the new mid floor (posi-joists) is thicker than the old one. The professionals that provided my drawings and calculations for planning and building control approval did not seem to be aware of any of these issues. Through previous experience renovating an old house I anticipated the stone walls disturbance issue and had the confidence to completely veto the first design suggestion of building the entire new roof structure onto the new internal timber frame which would have increased the loadings a lot and needed even deeper excavations for stronger footings alongside the old walls. The trouble with a mixed newbuild/renovation is you never quite know what regs you need to adhere and what will be relaxed. Not everything was resolved before work began so things that changed as the work proceeded meant asking the authorities for a clear in-writing answer and they have often taken weeks or months to respond. Building control insist that if an element like a mid floor is replaced in entirety then that new floor has to adhere to full regs. So that meant I couldn't re-use the existing really nice staircase (750mm clear width does not meet current regs) and the additional combined width of new stairs and wider upstair landing and corridor has added to the reduction in size of all the rooms (already reduced from the original sizes by wall insulation). The wider landings, wider door openings, extra landing space needed for future chair lift parking has made the new stairs steeper and right at the extreme limit of what is permitted and so a lot less comfortable to use. As there was no functioning sanitary equipment present in the derelict building the rebuilt shower and WC room in the main entrance lean-to extension had to fully conform to regs, basically had to be bigger, making the remaining space within the lean-to extension, the house entrance hall, already pretty minimal, smaller. Building warrant required putting 25mm diameter vents in the old stone walls every 1.5m. Achieved for all except the gable end walls (for which no drill long enough could be sourced) by purchasing 35x700 masonry drill, inserting 30mm (25mm internal) blue water pipe to line the holes. The drilling was difficult and potentially weakens the structure of the walls due to disturbing the loose stone fill which also falls in and jams the drill. The thicker gable end wall I put a single 4" drain pipe into located at the back of the fireplace where the wall is much thinner. This will also provide an air duct direct to the living room wood stove. PIR: As a test, I kept in my garage a leftover piece (made by one of the main manufacturers) from a loft conversion we did to our first house 26 years ago. 4 years later it had bowed noticeably and the edges had become crumbly. I vowed never to use the stuff again. When the builders were fitting it I queried the gaps I saw between the roof rafters and the cut edges saying I thought they should be filled with flexible sealant but was persuaded by them that it was not needed and when the Building Inspector agreed that plenty of ventilation was important I gave in. Nowadays it seems that people tape over the joins to prevent thermal bypass and in the hope it will keep it in place if it shrinks. Gapotape looks like a better solution. Whatever you do it may look great when it's fitted but particularly when directly under a roof that harsh heating and cooling cycle is bound to affect the foam on one side differently to the other side. And then there's the waste issue - it can't be recycled after end of life and there are quite a lot of off cuts to dispose of. With woodfibre and the like you can quickly and easily use a lot of your off-cuts because there's no precise cutting to deal with. 4 years on and some way away yet from finishing, in retrospect I would have left the original building as is, keeping it as a garage/store/workshop and self-built anew alongsided. Similar approach to what people have done for 1000s of years, when I think about it!

I don't understand this. The joists can't shrink/expand, relative to eachother, because they are fixed in position. OSB T&G4 has expansion built into the joints but they say that runs of over 7.2m should have a gap, in addition to the perimeter 10mm expansion, to avoid buckling.

So how do you deal with expansion/contraction over long runs? I'm replacing a 150yr-old mid-floor (inside rubble stone walls) done with no ply and no glue, so it all seems so totally overkill to me.

The joists run perpendicular to this partition, so I don't see how how it would affect the tying together of the joists. And they are already tied together at their ends by the external walls and in the centre by strong-backs. The partition over the top will help tie them together over the cut. The entire upper floor deck, 5m x 10m is already divided almost in two in the middle by the stair opening running 2/3rds of the way across and in the same direction as the joists. Also there needs to be an expansion joint dividing up the 10m run, according to the OSB install guide.

Probably no advantage in your case using more robust layers but I am finishing with only carpet and carpet underlay. Seems like a no-brainer to me though - separate elements wherever possible (unless perhaps you live in a seismic zone etc).

Thanks Dan. Looks like a good job. Was it specified by an architect? Puzzles me as to why not make the caberdek discontinuous between rooms. It's just a saw cut and would stop some transmission - a recommended design detail in a white paper from Canada I just read.

Thanks for the reply but I don't understand what you mean.

So the wall soleplate fixed straight onto the joists with only the Karma strips between?

Building an internal 100mm stud wall on a first floor (metal-web joists) deck to separate two bedrooms in a timber frame build. There will be no doors or sockets in the wall. Floor joists at 400 centres run perpendicular to the partition wall, ie. from under one room to under the other room. I will double plasterboard one or both sides of the partition, artight seal perimeters, install 75mm sound type mineral wool. (There are two other internal stud walls on this level but they both have doors in them so not worth as much effort in preventing sound travel.) For the purposes of reducing sound transmission between rooms - should I build the partition directly onto the floor joists and split the floor boarding (OSB T&G) between the two rooms or let the floor ply run continuous under the partition?

I have just fitted noggins using Z-clips between metal-web joists around an entire upper floor deck, using square twist nails as specified by the engineer and by Simpson the manufacturer. The Z-clip metal is soft enough that the head of the nail, if hit hard enough, forms a depression in the Z-clip and the underlying softwood, so the nails don't stand proud.

50mm between flanges seems a good solution.

It is described in the installation guide for posi-joists. (Not that it is specific to that type of joist.)

Thanks all. I've learnt a lot.

Is it better to break the floor deck (t&gOSB on posi-joists) between 2 rooms, in order to better isolate sound transmission between adjacent rooms? Or lay floor as a continuous deck and build the stud partition over this? 2nd option quicker/easier but speed is not a priority.

Quite, which is why the insurer's statement was a surprise. I mean, it just isn't practical to try and check the small print of the insurance policies of everyone that comes to do work. On the other hand, in theory it should mean my premium will be a lot less than otherwise since my insurer can pass much of their risk/liability onto other insurers.

I would like to know too. They are not at all suited to adding insulation, particularly since it would be very hard to get insulation into the space within the joists themselves.

Thanks @nod. Good to know. How about the other 'Contractors Insurance' ? I imagine that does not come cheap for them at all. Apparently it is law that came in in 2005 - maybe Scotland only.

I am half-way through a self-build / new-build / renovation project and I have just asked a broker to find a policy to cover. Even before submitting the project details to various insurers they say I should only use contractors that can prove they have £250,000 Contractors insurance as well as £5m Public Liability. This is so that insurers can fall back on those policies if there is any problem with the work done. They know I am doing some of the work and that I am not a professional builder. Anyone else heard of this requirement? Is every tradesperson used to being asked for this when they work on a site?

Thanks @Declan52. and @Oz07 for pics. I think it's clear I don't need to worry about a drain for the main exhaust. Good advice about insulating, (ie. you can't really have too much).

Ah, so it was an individual room supply pipe, not a main pipe to/from outside atmosphere?

Was the condensation forming inside or outside the duct ?

@2Declan52, thank you for the reassurance. Insulation seems like a much better way to fix condensation if it happens, than draining it.

I wonder if @Stones has a similar installation?

I have got my 1st fix install kit - everything except the MVHR unit itself (Vent Axia Advance S) - from BPC. They have been great. I have never installed MVHR before. It will be sited in a cold roof loft, above a corridor/landing that separates two bedrooms. Supply and exhaust vents (supplied by BPC) in a new sarking boarded slate roof. BPC provide a very good install guide pdf and almost everything about how to install seems clear except for some of the detail of how to connect the unit to roof vents. There are 2 bits in the guide that puzzle me: 1/. "Roof vents: In addition, roof vents must be installed at a higher level than the MVHR unit or condensation will form in the pipework. We recommend the installation of an in-line drain with waterless trap be fitted to the air extract roof vent to prevent water damage to the unit " Under the "Wall Vents" section however, it is says just to add a small FALL in the duct run from MVHR unit to the outside. No drain needed. I would like to understand why a wall vent needs no drain but a roof vent does. Why with roof vents the ducting goes upwards but with wall vents it goes down? How is an in-line drain fitted to 150 pipe? Is it just a tee-ing in of, say a 32mm waterless trap, into the 150 pipe at the lowest point and nearest the MVHR unit? 2/. "A short section of Insulated flexible ducting will be required to install roof vents..." Is this in combination with rigid 150 PVC piping which can only do set angles? If yes, then does it matter where in the run it goes - before or after the rigid PVC section(s)? If anyone knows of a photo of a standard loft to roof vents install, that would hopefully explain it all without a word!. Thank you, in advance.

A cheap DIY version of masonry stoves as used in Scandinavia.