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Cost effectiveness of insulation?

I'm surprised to see fairly little discussion of insulation on this forum - is there a reason for that?
Looking around the forum, the gist seems to be that a newly-fitted 4kW solar system on a typical house should be able to pay for itself in about 8 years, batteries are currently a bit of a non-starter, and ASHP/GSHPs - well, I still have to get my head around those and RHI payments.
But I thought the received wisdom was that insulation was the way to start? If we take an 'average' UK home with 85 square metres and an EPC of D, what does this forum think is the sensible way to think about insulation?
Obviously it is possible to insulate a modern home to the extent it'll barely need heating at all. But I'd suspect at that point it's beyond the law of diminishing returns and isn't cost effective.
I think anyone would agree that going around and sorting out obvious gaps and drafts cheaply is well worth doing.
Is it the case that because there isn't a specific 'product' that you can buy, that it's difficult to recommend between different homes.
Would be really interested in this forum's insight on this!
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  • Martyn1981Martyn1981 Forumite
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    It doesn't get said as much now, as it is hopefully in everyone subconscious, but the mantra on here used to be "insulate, insulate, insulate". I don't think that has changed, but perhaps just as we used to talk a lot about LED lamps, we now take it for granted ...... but you are right, it should get mentioned more.

    And for heating needs, especially if considering a change to the current system to one that is more environmentally friendly, it's always best to aim for a system that will provide the heating needed after all drafts and insulation upgrades have been addressed.

    The latest episode of Fully Charged was excellent, it looked at a house (a massive house) that really doesn't need heating because it was built to such a high insulation standard.

    Can you HEAT & POWER a big house with RENEWABLES?

    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • PetriixPetriix Forumite
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    Insulation is pretty intangible when it comes to ROI. Beyond adding loft insulation, it's not something you can easily buy or install without serious disruption or expense.

    We've got an area of flat roof which is poorly insulated. To bring it up to modern standards I would have to remove the ceiling along one edge to insulate between the ends of the joists, then add 130mm of rigid insulation above the deck before adding a second deck and felting on top. That's a massive job that would cost £thousands and save £tens from my heating bill.

    It makes sense to insulate properly when building or extending but it's much less clear when thinking about retrofitting. 
  • edited 15 June 2020 at 1:14AM
    HexaneHexane Forumite
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    edited 15 June 2020 at 1:14AM
    Received wisdom that insulation and energy efficiency is the place to start, is correct. The EPC is a notoriously vague way to measure this. However it's reasonable to say that you should look at getting basics in place of double glazing throughout, cavity wall insulation, at least 2500mm or 2700mm of loft insulation, draft-proofing where possible, radiator TRVs and heating system thermostat and timer controllers, and an efficient gas boiler, before looking at adding solar panels or similar.

    It is not widely accepted that a newly-fitted 4kW solar system on a typical house should be able to pay for itself in about 8 years. It might be 16 years or it might be more. But a solar panel installation is currently believed to be more likely to pay for itself than a battery installation. GSHP are disruptive and expensive, a wet ASHP system might not work as well as some people would like, and air-to-air ASHP systems like some on this forum have installed, aren't eligible for RHI payments.

    In my situation I already had all the insulation basics, bought one large draft excluder and some additional curtains, blinds and rugs, fitted LED lamps almost throughout, TRVs throughout where appropriate, and left the ancient gas boiler as-is because I wanted to spend the money on getting lots of solar panels before the FiT scheme ended for new installs (which it now has.)

    You may find that doing some of these things, and perhaps a boiler replacement if appropriate as well, would move you from an EPC D to an EPC C, but most purchasers don't care about the EPC rating anyway.

    It is largely in the hands of fate whether my next investment in energy efficiency will be a replacement gas boiler, a hot water cylinder with two immersion heaters instead of one, some means of linking the underfloor electric heating to my solar diverter system, an air-to-air ASHP setup to augment the gas boiler and provide air conditioning, or a battery electric vehicle with at least 60kWh battery capacity (to be charged partly via solar diverter.) A home battery system is a nice-to-have on the distant horizon but isn't economically tempting for now.

    My previous EPC report thought that solid floor insulation should be somewhere in my programme of work, but it doesn't seem very exciting so haven't really looked into it.
    7.25 kWp PV system (4.1kW WSW & 3.15kW ENE), Solis inverter, myenergi eddi & harvi for energy diversion to immersion heater. myenergi hub for Virtual Power Plant demand-side response trial.
  • silverwhistlesilverwhistle Forumite
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    I think by the time most of us got round to solar panels we'd most of us done the insulation, or at least the worthwhile stuff as Petriix has observed. It was a  requirement to get the FIT to have a certain EPC, as I vaguely recall. This year's improvement for me were new lintels at the back along with a new back door, which will mean a much less draughty kitchen and no more danger of the handle coming off in your hand, yet again..
    Beyond that it's difficult: cavity wall insulation and LED lights already, decent loft insulation although a new pre-insulated hatch (as opposed to my bodge) would be ideal. I might get a stand alone MHRV unit for the bathroom but my next major investment will hopefully be an EV with the reckoning that with PV and a time-of-day tariff I could get my fuel costs down around £8 a month.

    Think you'll find that if anybody comes on here and talks about doing up a house that insulation is always mentioned first.

  • joefizzjoefizz Forumite
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    I think anyone would agree that going around and sorting out obvious gaps and drafts cheaply is well worth doing.


    One of the biggest differences I have made is to increase the insulation in a 1980s timber framed bungalow.
    I couldnt do anything about the wall insulation (well I could but it would have meant removing plasterboard and replacing, something I originally planned to do but when I did it in an outbuilding I thought better of doing it in my house!).
    When redecorating a couple of years ago I put in increased floor insulation. Had originally used that thin roll type stuff under laminate over a concrete floor but when redecorating removed the skirting boards, bridged the gaps to the plasterboard with non wicking material and raised the floor height with solid insulation boards then put the roll type stuff on top. I was replacing all the sockets and extending some of the wiring as well so made sure all the gaps behind the sockets were air tight.
    Id had pvc windows put in about 15 years ago and some of the gaps around them left a lot to be desired so used frame filler to fill in all those gaps and replaced the horrible looking pvc sills with reclaimed wood ones.
    Anywhere there was an exposed outside facing wall I had a look at to see if I could do secondary insulation (so extra insulation behind tiles in outside bathroom wall and then other places like honeycombed blinds to reduce etc.
    Even things like cold bridges behind ceiling coving in the living room were addressed and loft insulation is already in the realms of at least 50cm, all done piecemeal with insulation on offer, rolls picked up cheap from gumtree etc etc.
    That gave me the good starting point and along with flushing out the system, fitting a magnetic filter, thermostatic valves on most of the radiators and stripping them down to bare metal and repainting (dont know if that really helped ;-)) reduced my oil heating usage to almost half.
    I put in a positive air system (drimaster) above the main radiator (non trv) in the hallway and other than sometimes drying out too much its been all good since. The biggest leak in the house now is the letterbox, although Ive fitted a new internal brush and internal flap (sorry postie!). Thought about building a porch on the front of the house but thats definitely overkill!
    It was only then I put in the solar, the batteries and then the ashp and have reduced my oil consumption down to a third of what it was a few years ago. Only just come off the oil again this week as it has been quite cold at night here (too low for the ashp - north face of a mountain in northern ireland).
    Was it cost effective? Well in the long run it probably would be and I wouldnt advise anyone to strip their house to its shell and redo from scratch all in one go ;-) But saying that if you are redecorating piecemeal anyway, its worth bearing in mind.
  • PetriixPetriix Forumite
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    That sounds like quite an undertaking! 
    I don't think the combination of the positive air system and sealing up gaps is the best idea; the positive air pressure has to go somewhere and it introduces cold air to the house. Instead you would benefit from some kind of heat exchanging ventilation system.
    Did you use some kind of special equipment to identify the cold spots or just work systematically on known areas?
  • I'm surprised to see fairly little discussion of insulation on this forum 
    I tend to notice draught-proofing being under-represented.  Although mentioned by yourself and other posters in this thread, on other boards, people often talk only in terms of insulation (whether draught-proofing is assumed to be included in that, who knows).  Draught-proofing is surely more important than insulation as a first consideration; a draughty house will be harder to heat than an under-insulated one.
  • pinnkspinnks Forumite
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    I had already done the LED thing, have super double glazing and cavity wall insulation, etc so splashed out 5 years ago on upgrading the loft insulation from a sagging 1980s nominal 100mm, that didn't even reach the eaves properly, with 300mm (200mm plus 100mm at 90 degrees) laid on top and the flooring raised on plastic stilts.  I added eaves vent protectors to ensure the new insulation did not block air flow.  Was it worth it?  Jury's still out on that!!!

    It is incredibly difficult to measure energy savings as weather conditions are so variable year on year but I have certainly not seen a sustained saving or downward trend.  Average annual gas before the work was about 9,500kWh; after the work it has varied between 8,600 and 10,300, so the average remains around the same. 

    A downside that I still haven't managed to resolve is condensation, both in the house and in the attic.  Before adding the 300mm and blocking some holes in the ceilings (some poor workmanship from original build and some made later with recessed lighting etc) I never had any noticeable condensation in the house and the attic was bone dry.  The windows rarely misted up at all.  In the winter immediately after adding the insulation I got water dripping off the felt and woodwork in the attic and condensation running down the windows and to some extent the walls in the house.  Mould has formed around window recesses and they are visibly damp. Nothing else had changed in the house to cause this! 

    This year I decided to remove the outer-most top run of insulation (runs parallel to the ridge) and removed the eaves vent thingys on the basis that they actually restrict airflow by 50% because of their corrugated construction and restrict the amount of air that can get into the attic because they are about 30cm long/high.  My guess is, they may be restricting airflow by perhaps 75%. Hopefully increasing airflow into the loft will solve things but if it does not I am tempted to remove the whole lot (and even poke the holes back in the ceilings...).

    So, not sure I would spend the £1,500 or whatever it cost (the stilt system was most of that) if I had my time over again...    
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
  • edited 19 June 2020 at 12:06AM
    markinmarkin Forumite
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    edited 19 June 2020 at 12:06AM
    Petriix said:
    Insulation is pretty intangible when it comes to ROI. Beyond adding loft insulation, it's not something you can easily buy or install without serious disruption or expense.

    We've got an area of flat roof which is poorly insulated. To bring it up to modern standards I would have to remove the ceiling along one edge to insulate between the ends of the joists, then add 130mm of rigid insulation above the deck before adding a second deck and felting on top. That's a massive job that would cost £thousands and save £tens from my heating bill.

    It makes sense to insulate properly when building or extending but it's much less clear when thinking about retrofitting. 
    Cant you just cut open the roof to insulate between the ends of the joists.
    .......

    Cavity wall at around 2K? is possibly a 15 year payback, Im sure Ive read going over board with insulation means the pay back will be 80+ years,  Isn't external insulation around £12K so again very long payback, DIY internal insulation room by room seems the most cost effective.

    ...................................................................................

    25-40 years - 25K to 50K 


     
  • joefizzjoefizz Forumite
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    Petriix said:
    That sounds like quite an undertaking! 
    I don't think the combination of the positive air system and sealing up gaps is the best idea; the positive air pressure has to go somewhere and it introduces cold air to the house. Instead you would benefit from some kind of heat exchanging ventilation system.
    Did you use some kind of special equipment to identify the cold spots or just work systematically on known areas?

    I knew I was never going to seal everything and there would be leakage over time but figured that positive air would perhaps have the air leaking out rather than in ;-)  The air flow then comes from a central source but on a windy night without the chimney sheep in you can really feel the draught coming down but only at foot level. Simple things like the chimney sheep (thought about balloon etc but too much faffing around to put up and down for spur of the moment fire lighting) made probably more of a difference than the loft insulation. The ventilation outlet is less than 2 metres from the front door and directly above the living room air vent for the fire so should be positive pressure on those most of the time. Of course like last night where external humidity is 90% it doesnt help much ;-)
    Tying in with pinnks later post, the cold spots were showing up as mould areas, very noticeable in areas behind coving etc and now its only on windows but Im not going down the triple glazing route. I did put the stretch plastic window film on the inside of the double glazing (attached to cover most of the pvc) and it has made a difference, pushing the mould back to the top corner of the bedroom where I think mice or birds have taken some of the insulation from the extreme corner and used for bedding. Not much chance of me being able to reach that without taking roof tiles off! The positive air system has virtually eliminated mould and kept the house at a low humidity, so much so that Im using a humidifier in the office most days to keep the humidity above 50% (gets uncomfortable on my eyes staring at screens in below that).
    I do have access to a thermal camera but only used it during the build stage, so for example I was surprised to see a gap in the wall insulation in my spare room so rather than rip the wall apart I put some wood cladding (as is common in certain icelandic houses) on the main outward facing wall with an air gap and with the reduction in humidity theres less chance of mould buildup, or at least less chance of it going unnoticed.
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