MortarThePoint

Castellated panels aren't cheap of course. About 6x as expensive as clip track. Are you figuring the trays will protect the insulation from the screed and therefore no need for the polythene. That may be a risky assumption, what do others think?

If you've ever been in any doubt, I do make this stuff up as I go along ? I do think it's useful though. There's a window with a U-value of 1.2 and an area of 1m2. "£3 per U per m2 per year". That window is costing me £3.60 of lost heat per year. Windows are a bad example as they can create drafts as they are so heat leaky. How much heat lost through that bit of loft. U-value of 0.11 area of 15m2. "£3 per U per m2 per year". That loft is costing me 0.11*15*3=£4.95 of lost heat per year.

For my scenario* I can multiply a surface's U value by £2.85 and it will give me the annual cost of heat lost. Example, U=0.13 --> 0.13*£2.85 = £0.37 p.a./m2. Or dU = 0.01 --> 0.01*£2.85 = 3p p.a./m2 Quite handy for me to remember "£3 per U per m2 per year" [I know there's no such thing as 'a U' but it's a way of remembering it] 183days * 24h/day * 13K * £0.05/kWh = £2.85 [careful swapping between kW and W of course] * My scenario is dT = 13 Celsius, 6 months and an ASHP with adjusted COP of 300%.

I didn't realise how cheap Gas is and that makes the number lower still. It seems Gas costs around £0.03/kWh [1] so that marginal rate becomes closer to 2p p.a./m2 saving. Prices can change of course, but that would need a whole lot of change. https://www.ukpower.co.uk/home_energy/tariffs-per-unit-kwh I secretly hope someone points out I've missed a factor of 10 or something because spending an extra £5/m2 to improve the U-value by 0.01W/m2K is so far from being financially sensible (payback >150 years). Even knowing this, I find myself irresistibly drawn to improving U-values. Even the embodied carbon side of increased insulation is very debateable with decades of payback time, but that's another story.

That's right. The raw maths is: Heat Flow Q = U*A*dT Heat Loss E_heat = time*average_heat_flow = (days*24hours/day) * U * A * (Average_dT) For me average dT across 6 month 'heating season' is 13K (i.e. 13 Celsius) --> E_heat = (183days/yr * 24hours/day) * 0.13W/m2K * 1m2 * 13K = 7422Wh/yr = 7.4kWh/yr per m2. That is heat energy, to understand what I'll pay, I need to know how much heat costs me. Using an ASHP with a COP of 300% (reasonable) and an electricity rate of £0.15/kWh electricity, I can calculated that heat costs £0.15 / 300% = £0.05/kWh heat. 7.4kWh * £0.05/kWh = £0.37/yr per m2. It's all linear with U so to work out differences you can just scale that figure, so if the difference is 0.01 then the cost difference is (0.01 / 0.13) = 1/13 of £0.37/yr /m2. When I work this sort of thing out I keep thinking I am making a mistake, but it's how it works (at least for marginally changes on a good base figure).

Don' want to draw too much attention to this consideration as I know people's priorities are many and varied. In part it was a note for my own consideration of the pros and cons. Anyway, I made a mistake in the first sentence as it was supposed to be "Improving a U=0.13 area by 0.01 saves approximately 3p/m2/yr with an air source heat pump." The mistake is obvious looking at the next sentence, but I wanted to correct that. so: Improving a U=0.13 area by 0.01 saves approximately 3p/m2/yr with an air source heat pump. [dT=13C, U=0.13, 6mo-->7.4kWh/m2, E=£0.05/kWh --> £0.37p.a./m2]

2no. 100mm Omnifit Slab 35? That make up should be good and warm. R_ins=9.0. Is that targeting U=0.14?

I have 222mm rafters and need to leave an approx. 50mm air gap so was planning to use 175mm of insulation between the rafters and 75mm under the rafters (all Mineral wool). Here are some example build ups: 75+100+75mm Rafter Roll 32, R=7.81 cost £35.75/m2 90+90mm FrameTherm 32 and 75mm Rockwool 38, R=5.63+1.97=7.6 cost £21.09/m2 [NB: RockWool not Formaldehyde free] 180+70mm Rockwool Flexi 35/38, R=5.14+1.84=6.98 cost £12.23/m2 [NB: RockWool not Formaldehyde free] 90+90+90mm OmniFit Slab 35, R=7.71 cost £12.15/m2 90+90mm OmniFit Slab 35 and 75mm DriTherm 32, R=5.14+2.34=7.48 cost ~£14/m2 90+90mm OmniFit Slab 35 and 60mm PavaTherm 38, R=5.14+1.58=6.72 cost ~£16.50/m2 90+90mm OmniFit Slab 35 and 50mm EcoTherm PIR 22, R=5.14+2.27=7.41 cost ~£14.60/m2 120+50mm EcoTherm PIR 22, R=7.73 cost ~£22/m2 If I were to do it again I would 100% use counter battens outside the roofing membrane and fill the rafters. Improving a U=1.3 area by 0.1 saves approximately 3p/m2/yr with an air source heat pump. [dT=13C, U=0.13, 6mo-->7.4kWh/m2, E=£0.05/kWh --> £0.37p.a./m2]

For the garage, BG FireLine MR was hard to source so I went with GTEC Fire MR from abcdepot. The 15mm GTEC product has the advantage of being 2400 sheets rather than 3000mm. Whilst sourcing that I got confirmation from BG and Siniat (GTEC) that their standard moisture resistant plasterboard can be considered in the same way as their standard WallBoard when it comes to fire considerations, in theory. Untested though, but those statements were suffice for my BCO.

Duraline does appear to be available despite the BG website indicating otherwise at some point. Duraline: "Designed to provide enhanced sound, fire and impact resistance" 15mm only, 13.9kg/m2, TE only, 1200 x 2400/300 So almost as high area density as Soundbloc F (14.1kg/m2) but adds impact resistance. I've been quoted 1.2% cheaper than Soundbloc F. (~£14+VAT/sheet). As such, pit probably makes a better choice for walls though consider Habito instead for fixability. What to use under rafters in an attic is interesting as you probably want some impact protection, but ideally not the weight.

Ordered the TradeLine one at £2.35 per 3m length which is cheaper than 100x22 timber

On paper it's the other way round. TradeLine claim 0.5mm gauge and BG claim 0.45mm. Probably the joys of tolerances at play though which means the TradeLine is the thinner as you say. <rant>'Tolerances' is one of the great deceptions of the construction sector as far as I am concerned. Most other lines of work the nominal is what the manufacturer tries to achieve so sits in the middle of the distribution (mean) and the tolerance sets the width of the tails either side. In construction supplies, many seem to treat it that as long as X% are within nominal +/- the tolerance, they can reduce the mean to save money. Hence 100mm blocks actually being 96mm etc. It's a con in my eyes.</rant> British Gypsum: TradeLine:

I like the look of the Tradeline ones

British-Gypsum and GTEC resilient bars are about twice the price of lesser brands like Tradeline/Libra/Speedline/Phoenix. thickness and dimensions seem the same, so is that just the price of branding at play. I should imagine its all the same isn't it? I prefer the look of bars that have the acoustic holes away from the fold, but given the fact that both premium (BG) and budget (Libra) have holes on folds it doesn't seem an issue. Knauf double up and do both. SpeedLine: TradeLine(secondary source? Siniat GTEC: Gypframe: Knauf:

Looks comprehensive. What was the airtight paint you used?

Poly bead (e.g. Ecobead) cavity wall insulation with Cavalok cavity closers. Mineral wool (Knauf) at rafter level. Mineral wool (Knauf) at ceiling level and any flat roof bits.

At the skirting junction and the ceiling cavity, should I think about some form of sealing paint or put some wet plaster on at an early stage in those areas?

A type of spray foam like this?

Hopefully resolved by the Compraband, but I expect I may have to use a sticky membrane too. Something like Tescon Profil though difficult to appreciate how much better that is than duct tape. A lot easier to fit with the backing paper.

A bit confused, isn't that what air tightness is all about, stopping warm air leaving and cold air entering? All the airtightness measures would mean that air is only coming in and out where intended, through the ventilation system. Taking the rafter insulation as an example, the plan is a ventilated cavity above mineral wool insulation and then a VCL. Air fro outside will get on to the insulation, but hopefully not through or around the insulation to the warm side. Brick and block walls. Hopefully that makes airtightness in that area as simple as wet plaster onto the blockwork walls.

I'm keen to stay on top of the airtightness as I move forward with the 1st fix and beyond. I am new to thinking about most of this for forgive the inexperience. I'm thinking of leakage as being mostly through surfaces and edges/junctions. Surfaces: wet plaster on the blockwork walls (GF and FF) wet plaster on the plasterboard 'walls' and ceilings of the attic liquid screed on GF and FF Windows themselves are constructed with a good L-value and have not trickle vents Edges & Junctions Considering all the junctions between surfaces: Skirting area (GF & FF) - There is a strip of blockwork around the outside of rooms that is below where the plaster will go. This is where the screed expansion strip sticks. I am fitting the expansion strip to the blockwork wall and then taping the membrane that goes under the screed to the skirt of the expansion strip. That leaves a 'gap' between the expansion strip and the blockwork. Narrow but very long. E.g. 10no. 4x4 rooms with a 1/4 mm gap gives an area of 40,000mm2. Has anyone done anything about this? GF ceiling void - I'll use a sealant between the plasterboard and the walls, but that still leaves a 60+ mm high strip of blockwork and the underside of the hollowcore slabs with no airtightness. measures. Window & door frames - I'm considering using a triple action compraband for this, otherwise a membrane with a sticky strip that sticks to the frame and gets plastered over. Below rafters - VCL with taped joints. Ideally run all the way from wall plate to wall plate and taped to the wall plate all round. Tricky as there is a layer of insulation here too (~100mm at attic floor level). Hollowcore - I have attempted to seal the wall cavity ends of the cores of the hollowcore planks. No access realistic now. I'll seal the leaving space ends of the hollowcore where feasible. There are ~10mm dia. drainage holes that pass vertically through the hollowcore. At the top these will be sealed by the screed membrane. At the bottom I'll probably plug then with something porous (e.g. scrunch of mineral wool insulation) Wall plate - covered by plastering of VCL taped to it. Light fittings - If there other junctions listed above are sealed well then these shouldn't matter so much. For down lighters I'll try to use the types of cover that are designed for use with insulation. Sockets - I'd like to seal the cable entries. What have people used for this? I'm not keen on using a mastic type sealant as that would make any future work a nightmare. A sheet material with holes for the wires cut more tightly would be nice. Loft hatches - insulated and sealed loft hatches to be used. Loft hatch frame taped to ceiling VCL before plasterboard being added. Extractor fans/ventilation - Any not constant extractor fans will need to have a spring loaded damper to close them off when not running. Cable and pipe feeds - Spray foam would be the obvious choice. Otherwise mineral wool insulation. Any areas I have forgotten about?

Thanks Peter, so sounds like another bonus. I can see the downside of spiral/snail if using clip tracks as they wouldn't all be aligned in the same direction, but with castellated panels it seems like it would be straight forward. It doesn't use any more pipe does it? You don't happen to know if Wunda are able to design it as spiral for me?

I've sent back the previous lot of pipe and am changing to PERT-AL-PERT instead. To maximise my chances of success I am also likely to be using castellated panels. Further, I am thinking of changing the layout to snail pattern as this replaces a large number of 180 degree bends with a larger number of 90 degree bends and one 180 degree bend. The benefit is that those 90 degree bends are easier to form and less likely to store residual stress. Does anyone know any pros and cons of snail pattern over the more conventions pattern?

I'll leave space for a piece of plasterboard and plaster at the top of the brickwork of the inner leaf. One reason to not put the outer rafter in the cavity is to allow a second timber for the angled plasterboard to mount to. Crazy, but I may end up with three rafters as I am keen for the Brickies to have a line to follow with their outer leaf brickwork.

Should have looked at your plans first. No windows on the elevation facing your parents. Is the planner OK about the distance to the building to the West? I presume it's a building. It could be about right to daylight? If so the orientation of the duo pitch roof could be rotated by 90 degrees to put an eave on the North elevation and from a daylight perspective that lowers the roof