Archer

I've calmed down slightly from yesterday. Odour in the room has significantly reduced and I'm currently ventilating, heating and exploring a dehumidifier to see if there is generally a problem with high humidity which might be solvable. Weather over the last few weeks has been cold and wet which isn't a great combination. Think before I go ripping out any work, it's worth a bit of a pause to see if a few common sense measures can address the issue. Realised as well that I could take off the vapour impermeable paint easily as well if needed (it's shellac based so sponging with alcohol will easily remove). Also not sure that the issue isn't a different wall - the east facing external wall that we didn't add IWI to and is therefore colder. Going to see how I get on with this and hopefully get it sorted

It's not done with a membrane because obviously a membrane outside of plasterboard wouldn't work. In principle it should work with a painted/ coated layer. There are examples of this that you can find (it's not an ideal comparable, but think of a liquid dpm - this does the same job as polythene for example). We've used a similar technique elsewhere in the house with no issues... The problem here seems to be the plasterboard sandwich behind it (at least I'm assuming). Do you think perforating with drill holes and then filling and decorating after allowing some time for the moisture to escape could work?

Yes that's right, timber frame walls are original. We basically added the insulated plasterboard over the top (made a sandwich like you said). Yeah I checked the buildup and the software was happy so I assumed low risk. Wondering if the plaster wasn't fully dry, seems funny that it could have accumulated significant moisture so quickly but either way unless the smell is caused by something else that seems to have happened

I'm worried it might be as well because I've possibly locked in any moisture between two impervious layers (the original polythene and the new top layer of paint). I'm not sure about the issue you've described though, because the VCL should ideally be on the outer surface (warm side) of the wall? In my head, the issue is the old polythene layer now behind the top layer of insulation

Hoping to get some advice on a situation in our 70's house renovation. Cheers all in advance, this one is stressing me out a bit... So, situation as follows - we've just stripped the wallpaper off our daughter's room and had the walls and ceiling skimmed. No smell in the room before the work was undertaken in the first week of Jan. On the outside, north facing wall we added a layer of internal wall insulation. The wall build up is (from outside to in) - cedar shingles on battens and 10mm ply sheafing, 90mm timber frame infilled with mineral wool, polythene vcl, plasterboard and to that we added 40mm PIR insulated plasterboard screwed to the studs through the existing plasterboard. After the walls were skimmed and dried for a couple of weeks I sealed the wall with Zinnser BIN paint to act as a mist coat and new VCL on the outer face of the new plasterboard... Now we've noticed a rank, musty smell coming from the room and in particular from that wall. I'm assuming that it must be interstitial condensation, presumably between the new insulated plasterboard and the old polythene vcl. I'm desperate for ideas on what to do next. Checked this buildup was low risk with condensation analysis software (build desk) but must have cocked something up? Any building physics advice here - If I whack up the heating, is it likely to dry out the wall on its own, or would drilling regular small holes through the plaster/insulation & polythene help? We have an central A2A heating system so could also introduce a positive air pressure in the room to reduce humidity and force air and moisture out through the fabric. Really want to avoid having to take everything off and starting again on the wall which would be a disaster. Hoping for reassurance...

Thanks for the suggestions, this is really useful. I've abandoned the idea of laminating something myself... Working out the number of panels that I'd need and it's a lot of work with uncertain results. The company linked above looks pretty much exactly what I'm after with the XPS and 4mm ply facings. The "Tekwarm" loft boards are similar but with PIR and a single 8mm OSB facing.

Ok, if it's of use to anyone else - there does still seem to be a breathable, perforated EPS insulation board available, which could be another option for me. Baumit Open Therm https://baumit.co.uk/products/external-wall-insulation/opensystem-breathable-ewi/baumit-opentherm

Yup, very drafty loft for sure. Between the rafters are already filled with mineral wool. We will be boarding 50% of the width of the loft and half of the length, so much more than a few feet. The risk I was imagining is warm, moist air from below rising and getting trapped on the underside of the insulation and possibly rotting the rafters. I don't know if this is imagined but there a few horror stories floating around online and surveyors recommending that foam type insulation is removed from lofts... I think problems are probably unlikely and rare and that I'm overthinking, but still. You're right though, PIR would be twice as effective thermally for the same depth of insulation. They used to sell a perforated "vapour open" foam board, but I can't find it online any more

It's an older 70's house so not a new build. Loft hatch is very limited in size. I can get all the timber and cork cut to size though

Again, really limited understanding of the structural theory... But I thought that the core material mostly acts like a web to keep the two face materials apart. Hence being able to use quite weak stuff like EPS. Cork insulation is quite strong in compression, but not in tension.

Merry Christmas everyone. I know this is a bonkers idea before I've even typed it out from my sherry addled brain. Anyway, let rip, I can take it. Thinking goes something like this... 1. Want to board a section of my loft for easier access and light storage; 2. Head height is very limited (about 1.4m at the apex; 3. Rafters are about 8cm deep at 50cm spacing (I think, need to remeasure) 4. Worried about adding too much weight; also want to make sure that any insulation and boarding is vapour permeable 5. Want the easiest DIY option possible - loft is not a nice place to work Now obviously loft legs with mineral wool underneath and 18mm OSB is the obvious choice. However, I've been idly thinking that finding a way to screw an insulated panel directly to the rafters would be more straightforward than faffing about with the loft legs, balanced between rafters... There are PIR options for loft floors with foam insulation laminated to a single sheet of 18mm OSB. The weight of these is 12-15kg/m2 so I might only be able to safely store another 5kg doing this... Also, I'm not sure how rational it is but it feels risky to encase a section of the rafters in impermeable foam in case moisture vapour from below rises and gets trapped. (Any thoughts on this risk?) So... I've been wondering whether, structurally speaking, you could DIY a breathable "Loft SIP" by laminating 2x face sheets of either 3mm or 6mm hardboard either side of a 80mm cork insulation core using D4 adhesive or something similar. 3.2mm hardboard is obviously incredibly flimsy by itself, but am I right that in a sandwich panel, the thickness of the face material is less important, because it's acting like a flange (ie. in a metal SIP for eg.). The panels would only need to support the weight of a person across a pretty short span... Still, don't want people dropping though the ceiling! Is there any straightforward way to calculate this or is it just flat out a terrible idea? I was thinking to mock up a single cork SIP panel with some offcuts and test it but happy to get some science before going further! Cheers

I'm still trying to get my head around trying to size the inverter. Our ASHP (12.5kw) says it's power output is 4kw or 19amps. I'm assuming that would be the max if it's working flat out for a period? And then we'd want to allow for an electric oven/ induction hob (3kw?!) and maybe some spare capacity for adhoc things... But an 8-10kw inverter seems much bigger than almost everyone has so I'm assuming that I'm misunderstanding and most appliances only draw the peak for a very short time, is that right? I'm getting some expert advice now, but it seems to be that 5-8kw inverter is probably the sweet spot for our usage. Does that sound about right?

Good luck with it all however you decide to progress. Our house is also 70's and we ended up keeping the ground floor steel ducts and adding a second zone in with new ducting and vents from the ceiling in the first floor. Obviously with heat pumps the supply temperature is much lower than gas warm air so you need to run the system for longer essentially to achieve the same input of heat. Most of the time this is beneficial because you can get the same level of comfort at a lower set air temp when the system is running. Ours feels a tiny bit underpowered when it's really cold. It still gets up to temperature but it takes hours to do so. Only seem to notice this at freezing and below, I think because of the heat pump defrost cycles and generally greater heat loss ( our house isn't that well insulated) I'm still not entirely sure how we got it wrong. The A2A heat pump itself is oversized so should be fine. My suspicion is that the 2 indoor air handlers are too small because the upstairs duct work is custom made so unlikely to be the problem. Either way, it's a bit annoying but otherwise the retrofit has worked fine. Much better than the 70's original gas system we replaced.

This is all really helpful stuff, thank you. Just to add that I think the restriction on VAT to solar installs has been lifted - at least according to this. All battery installations are now exempt (is this right?) https://contact-solar.co.uk/blog/uk-government-scraps-vat-on-battery-storage/

I'm normally sceptical but Fogstar seem to be well rated for budget batteries. Uk customer service, long trading history, lots of previous customers etc. Not as dodgy as it seems. But also riskier than getting a big brand through a well known installer

Definitely getting warmer I'd say. By the time you've paid for an installer and with real life / non Nirvana usage, it would likely be a 5-6 year payback. But that's decent given it has an 8 year warranty and should last 10+ Feels like a good deal, but still brings me back to trying to work out how to get a decent installer who would fit one and know what they are doing to get me started on the energy management side.

That's the one! Well a chap on Money Saving Expert reckons he's got an "all in" price of £4.5k and that was based on buying the Fogstar for more (£2500). Feels quite daunting to find an installer though unless anyone has suggestions https://forums.moneysavingexpert.com/discussion/6457277/fogstar-home-batteries-domestic/p5

Also, another thing I don't understand - from reading other posts it seems there are efficiency losses between the grid, your battery and your home. Is it easy to quantify what these losses are? I've seen people use 10% to 25% which is quite a big range

No, this is what I needed to understand and is really useful. All of your risk points are totally valid. There is also the question about whether the technology now gets superceded quickly by something better/ cheaper and also whether increasing adoption flattens out the difference between peak & off peak power demand. You can get interest free finance and 10/12 year warranties which reduces some of your risks above but obviously not completely. I'm not sure if I'm allowed to link products in forum rules, but there is a 15.5kw Fogstar home battery with great reviews that is currently retailing for £2000. Changes the payback to 4-5 years but (allowing for the inverter and capable electrician to install). Does anyone have any experience with DIY installation - it's definitely beyond me but I'm not sure how to go about finding someone who will be comfortable installing this sort of kit...??

Putting the environmental arguments to one side for a moment, I could use some advice on how strong the business case is for home batteries in our circumstances. Our house is not well insulated by Buildhub standard - it's very much average for the UK stock with around 70mm mineral wool in walls and floor and a better insulated attic. We have a heat pump running heating and hot water but no solar PV (partly because of shading and partly cost). I estimate on our current tariff we're spending around £1300 a year on electricity at 23p/kwh and perhaps around an average of total 16kwh per day (if my calculations and understanding are sound... always a danger). Installing a 13.5kw home battery seems to cost around £7.3k with an advertised saving of £900 per annum which is maybe a bit optimistic but feels broadly in the right ballpark (if we can get most of use through the battery at a time of use tariff around 8p/kwh) So perhaps a 9 year payback on the investment? Not spectacular but pretty solid and with the added benefit of some protection in the event of a powercut. Advice appreciated - are my logic and sums above ok... what are the gotchas here?! Compatibility with high demand heat pumps, risk of the future Time of Use Tariffs being less generous, sizing the battery for winter peak demand or summer use...? Thoughts appreciated

I've just fairly recently installed a ducted A2A system (mostly retro fit of existing 70's gas warm air). I can confirm that it's virtually silent in the bedrooms, haven't noticed a major difference in comfort from the radiator/ wet systems that we've had in other houses but with the benefit of the option of cooling. The supply air is still "warm" but not as hot as that coming from the gas warm air system it replaced. If anything this is an advantage - you get a much longer, gentler heat and it modulates the fans up and down as it nears the target temperature. Our system is a 2 zone VRF - which is overkill, but was done for noise reasons and the outside unit is very quiet most of the time - barely audible from 5 metres, despite having a Sound Power rating of 70db. Biggest negative is the amount of space the fan units and plenum's take up; also the lack of grant and general wild west nature of AC installers. There are plenty around but trying to find a good one...

I think in principle that should work, the larger VRF systems are hideously complex (any large scale MEP), but we had the same need - to separately control each zone/ indoor unit and to have a single outdoor unit (mainly because of space and noise issues). It was surprisingly hard to find a unit that ticked all of the boxes. Many of the multi-split's seem to work off a single control (ie. you can't adjust each flow separately). The VRF branch box is a neat solution - hopefully it won't turn out to be hideously unreliable or hard to maintain. It looks quite straightforward and the piping for ours at least was very simple. Just seems that there isn't really a market for smaller VRF / individually controlled systems at the moment, hence the lack of choice.

Just to add that we have a 14kw residential scale VRF system (Mitsubishi Electric). It's a City Multi ducted A2A system so probably designed for small retail or office units primarily but works fine - we have 2 indoor units running off a single outdoor unit with the intention to add a 3rd in the future which this gives us the flexibility to do easily. There is an indoor junction box which controls refrigerant flow between the indoor units and the outdoor. It was about £500 more expensive than the equivalent non-VRF multi-split but has a lower operating noise (not sure why).

That's helpful @severnside and also a bit worrying from my perspective. We are still waiting on planning (looooonnnnngggg story) but will be retro-fitting warm air in a similar way to you. How has the cost compared with your old oil fired system out of interest?

This unit does look perfect as a direct replacement. You still have an outdoor and indoor unit by the looks of things but it's very design led. The wall units are some of the nicest I've seen. Having gone through the mill on this with the current gas warm air providers (including J&S etc), I'd be a little wary of an unproven American import. The warranties all seem quite weak and you wouldn't get great aftercare support etc. The commercial A2A products are a bit niche, but Daiken, Mitsubishi etc do sell products with decent warranties and engineers that know what they are doing with them. Government should look again at A2A systems, they are not getting the support that A2W does and it makes no sense. HVAC has additional benefits to air quality etc that could really improve uptake imo