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Author Topic: internal wall insulation on a wall with cavity wall insulation already  (Read 653 times)
Mudman
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« on: November 20, 2020, 02:09:54 PM »

I'm advising friends renovating a fairly small 1960s ground floor/1st floor maisonette.

The gas boiler is knackered so a different heat source is needed anyway and they are considering ASHP with under floor heating in the hope that it's greener.
i've suggested this would work better if there was improved wall insulation- about half the perimeter is external wall, the rest is various party walls with adjoining flats.

Whenever i've been involved in internal wall insulation before it has been on solid walls, so the transformation was amazing.

My main question is, has anyone fitted IWI to walls with CWI in them, and are there any caveats to doing so?

There are other issues with ASHP, around fitting underfloor heating- they are considering fitting pipes in a new layer of screed in the ground floor, which appears to be an uninsulated concrete slab. i suggested that even a bit of insulation (10mm?) below such pipes/screed would only double the loss of headroom and be a lot more efficient. Any ideas? I'm thinkng that areogel would be very expensive and so un-viable...
The 1st floor floor is wood, so i guess fitting ufh pipes between the joists with spreader plates would be pretty efficient and straight forward , and the removal of radiators will offset loss of internal volume from the installation of IWI...   Also if these pipes warm the ceiling below, that might help keep the groundfloor warm without losing too much heat to the concrete slab...

for DHW, they were thinking of using the ASHP and installing a tank- i said it's not that good a use of an ASHP and they might do as well to have an electric shower and inline electric heaters.  that way there are no standing losses and they don't loose internal space to a hot water tank. Any thoughts here?

Thanks, folks, MM

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Alan D
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« Reply #1 on: November 20, 2020, 02:36:48 PM »

Ref  " The 1st floor floor is wood, so i guess fitting ufh pipes between the joists with spreader plates would be pretty efficient and straight forward "

The only down side of under floor heating with wooden floors is noise of expansion / contraction. When its heating / cooling
Not so bad with a heat pump because the working temperature is a lot lower. Best to install loads of pipe so the running temp
can be as low as possible.
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TT
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« Reply #2 on: November 20, 2020, 03:00:10 PM »

I would investigate getting the boiler fixed
Installing UFH/ Oversize reads as required.
Then insulating the house to the hilt
Then look at ASHP when the heating demand is lower due to the insulation
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Countrypaul
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« Reply #3 on: November 20, 2020, 03:49:51 PM »

We have cavity wall insulation (approx 70mm injected PUR) on the older walls but I also fitted rockwool on the internal side. We considerd fitting a VCL on the internal side but because of the PUR were advised not to so didn't bother. The walls were battened out 50mm at 400mm centres and 50mm rockwool batts fitted between, plasterboarded over and skimed. Can't tell you how much difference it has made as it was done as part of a major renovation.

Downstairs we have UFH in a 70mm S&C screed with pipes at 150mm centres fitted over 120mm pur on a B&B floor. Upstairs we have fitted from below UFH using spreader plates for the bathrooms (nothing in the bedrooms). The bathrooms have a 22mm chipboard floordeck and ceramic tiles. The bathroom floors never really feel that warm- but not cold either which they do otherwise - probably because we run the UFH at quite a lot temperature (<30C). Below the first floor UFH pipes is 100 - 200mm of rockwool. We also have electric towel radiators in the bathrooms on timer switches so they can be on a preset program dropping heating level over time.

If the place in question is not well insulated, I would seriously consider oversize radiators upstairs rather than trying to retrofit UFH.
We use an ASHP (mainly on E7) with a thermal store.
« Last Edit: November 20, 2020, 04:14:01 PM by Countrypaul » Logged
kdmnx
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« Reply #4 on: November 20, 2020, 05:53:24 PM »

Our house was extended before we owned it. The extension was cold. So I fitted new plasterboard that came with 50mm of PIR already stuck to the back. Along with other improvements (extra 300mm of rockwool above and triple-glazing), there was a noticeable difference.

I think your underfloor heating plan won't work. You need to do it properly by digging up the slab, fitting 100mm (minimum) of PIR, then laying the UFH pipe and screeding over. The deeper the insulation and the deeper the screed the more comfortable the room will be. Laying UFH pipe over the top of an uninsulated slab will result in the slab sucking away the heat faster than your ASHP can work. Upstairs I wouldn't go for UFH, just go for oversized rads.

Replacing the boiler with an efficient modern new one will be MUCH cheaper. As boring as that might be... 
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Countrypaul
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« Reply #5 on: November 20, 2020, 07:10:41 PM »

One aspect we have omitted to mention is airtightness. Having a well insulated property that relies on minimal heating also requires that the property is quite air tight, that normally means also incuding an MVHR system. Some MVHR systems include heaters to ensure the delivered air is already at room temp, some include heaters to minimise the HE accumulating ice and compromising performance.

Your first step sould be to perform an analysis of the current setup and work out where the heat is lost and how much sould be required, then compare against current usage and adjust your model accordingly.  You should get an air tightnesing air tights test performed as part of that process. Once you have done that you can see what effect various changes will have, such as tripple glazed windows and doors, IWI, ground floor UFH with and without replacing the exisiting floor, removing as many penetrations of the thermal enelope as possible, improvng air tightness and fitting MVHR (beware of improving air tightness without MVHR can lead to excessive condensation, mould and if retaining a gas boiler even Co poisoning.

Once you have a model howing the effects of each change you could put in the cost of each option and then see what is worthwhile.
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Mudman
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« Reply #6 on: November 21, 2020, 10:14:46 AM »

Thanks so much for the replies i'm going there again today so will see how far through they had thought the ASHP option, probably not much beyond the vague idea that the whole country will stop having gas boilers soon so lets not replace that one.

MVHR options will be limited as they cannot get into the ceiling above the 1st floor. Is it every possible to have a vent in a wall rather than ceiling or does that compromise air flow too much? i can imagine a way to get ducts to each room if the wall vent was possible.

IWI is what i will keep pushing. its the best long term option inso many ways, so long as they can find someone careful enough in fitting it.

Thanks again, MM
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Countrypaul
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« Reply #7 on: November 21, 2020, 10:55:07 AM »

Quite a lot of the vent positions in my house are on walls rather than the ceilings. The house is a dormer bungalow so the first floor has a lot of sloping ceiling, and where there are flat ceiings they tend to be quite low so all the vents on the first floor are wall mounted. In our case each vent has its own pipe back to a central plenum fed from the MVHR unit. I could imagine if using the system with a single pipe and various drops this would make wall vents difficult.
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Mudman
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« Reply #8 on: November 21, 2020, 06:45:04 PM »

Thanks, Countrypaul that's useful to know. why do you think that single pipe with branches would be harder on a branch with wall vents?

Vent positions on the wall should be on the opposite wall to the door really shouldn't they? the ceiling above 1st floor is concrete slab (other flat above) so its not easy to get anywhere near the opposing corner. Maybe can fit some ducts in stud walls to get most of the way there or something....

Odd thing is that the double glazing doesn't have trickle vents, even though it does not look ancient.

Digging up the floor seems so drastic but it's only labour and skip fulls of waste followed by a load of insulation, pipes and screed i suppose. ideally the insuation would be linked to the IWI on the external perimeter i guess. If they managed both floor and IWI the heat loss will be drastically reduced.  hmmm


Anyone got any comments on IWI on a cavity wall?

thanks again, MM


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Countrypaul
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« Reply #9 on: November 21, 2020, 07:14:30 PM »

I only have experience with the semi-flexible that runs from the plenum chamber to the outlets/inlets, but this is 70mm so easily fits in the stud walls we have on the first floor. There needs to be a balnce between input and extract, in our case 4 bedroom (input 1 pipe each except MB 2), 2 ensuite & 1 house bathroom extract 2 pipes each (only one ensuite used as teenagers gaming room) all on the first floor. Ground floor lounge (2 input), "playroom" (2 input), study (1 input) , garden room (1 input), kitchen (2 extract). utility (2 extract) and WC (1 extract).

The quote I got for a branched system used larger pipes (could not fit in stud walls) and needed to link each room in turn either extract or input pipe. In our case that made installation much more difficult. The branched system was also suposed to allow noise transmission from room to room  - but I don't know if that is true since we don't have a branched system.

Where the vents are does depend on layout, for the house bathroom the extract is opposite the door as it is for the MB ensuite. In two of the bedrooms the extract is on a wall at 90 degrees to the door but the furthest wall at 90 degrees, the other ones are on the same wall as the entrance door but at 90 to the ensuite(den) doors. Down stairsthe lounge and study are awat from the entrance doors, but the "playroom" has the input quite close as there is a large glulam beam that prevents the pipework going any further unless we dropped the ceiling another 3" which would be getting too low. The extract in the kitchen is close to where all the steam is likely to be produced, the WC extract is pretty much in the middle of a very small room, and in the utility it is close to the sink between the study door and kitchen door (yes the study is only accessed through the utility).  Most of the layout was designed by the supplier (Airflow in our case) but I ended up having to change the routing of the pipes as they had them going through some steels and through some glulams both of which our engineer said no to.

We did dig up some floors that were previously laid directly onto the ground - few bits of hardcore then 3-4" or concrete, not that difficult as we had a wall down and a digger on site at the time. We put in a Beam and Block floor to match the rest of the ground floor which required digging a little deeper than if we had just replaced the floor and added insulation. The B&B floor showed it worth later when we had to put a drain in that had been missed off the drainage plan and went directly under the area that was orginally concrete on the ground. All our foul drains go down through teh floor and out underground to reduce penetrations of the thermal envelope above ground.

The ground floor insulation below the screen has a 50mm PUR upstand at the edges that the rockwool batts rest on as you sugested.
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marshman
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« Reply #10 on: November 21, 2020, 07:37:03 PM »

Mudman,

I self built a house back in the late 1980's. It had underfloor heating (solid ground floor, timber first floor). Even back then I realised the value of insulation. It was fairly conventional build, 4" brick outer skin, 2" cavity and 5" thermal blocks (thermalite something or others). The cavities were filled.  After we had lived there for a while I thought that the north facing "back bedrooms" could be warmer so I "dry lined" the outside walls. 2" x 2" battens and 2" of fibreglass insulation all covered with 3/8" (sorry 9mm) plasterboard. It made a big difference, so big in fact that I did same to the lounge walls at the south end of the house and to the end walls upstairs. Instantly made the rooms feel warmer.

With regard to the UFH we had a 4" think concrete slab, 2 layers of "2L2"  insulation (2L2 is effectively 2 layers of bubble wrap stuck together with a layer of aluminium foil either side.), then a 2" screed in which the UFH pipes were buried.  The pipes were 20mm pex mounted on 12" centres (Wirsbo - now Uponor system).  Upstairs was the same with the pipes mounted in aluminium spreader plates under T&G floorboards.  Never had any issue with expansion noise.  Can't recall the u value of the 2L2 but I think I was told each layer was equivalent to 1" of polystyrene.

The house was toasty warm and really cheap to heat - we had a condensing gas boiler (Trisave Turbo 60) which must have been one of the first ones - I remember researching them at the time (not easy in preinternet days!) and being told by British Gas not to touch condensing gas boilers because they didn't work! In fact it was ideally suited to driving UFH as it always ran in condensing mode.  The only comments I would make is that UFH in concrete screed is slow to respond - very slow - and UFH under wood floor boards usually needs to run a bit hotter then in screed.

I also retro fitted MHRV as I had draughtproofed the house and condensation on the windows was becoming a problem - they were only 16mm units with wooden frames. The MHRV instantly solved the problem - I pretty much ran two back bones (1for upstairs and 1 for down) and just branched off to each room - same for extraction.

Our current house has UFH (Wirsbo - Uponor) again. Upstairs is the same as before, aluminium spreader plates under floor boards. Downstairs has 2" expanded polystyrene insulation over the 4" concrete slab. The pipes sit in spreader plates sunk into the top 1" of the polystyrene. The whole lot covered by floorboards.  The system used to be heated by a 20kW Hunter boiler stove (14kW to water and 8 kW to the room). A few years back I had a GSHP installed and the wood boiler stove was removed. During the heating season the GSHP runs 24/7 pumping water round the UFH at a nice low temperature. This keeps the house toasty warm 24 hours a day, 7 days a week. That is the key to low running costs, low temperature water and long run times, forget turning the heating on for an hour in the morning and 5 hours at night!  I also retro fitted MHRV to this house. More of a challenge as it is an old farmhouse with think walls but lots of careful thinking on routing of ducts and it works really well, all ducting is hidden.
  
With regard to the flat I would do the following:

1. Dryline and insulate walls (will also help with sound insulation)
2. If going for UFH, on the groundfloor I would use 2 layers of 2L2  (  https://www.thermal-economics.co.uk/main-products/alreflex-2l2/  ) and then 25mm PIR, celotex or what ever it is called between the UFH pipes and aluminium spreader plates and lay floorboards over the top - quicker, easier ands less disruptive than a screed.  (obviously you would need 50mm sq bearers to fix the plates and floorboards to, effectively crating a floating floor. Upstairs lift the floorboards fit plates and pipes and relay floorboards. If the joists are not thick enough to notch out at the ends to allow the pipes to pass round at the ends of the loops then you would have to lay so 3" x 1" timbers across at 12" centres to take the plates, this would then mean turning all the floor boards 90 degs before refixing.
3. Draughtproof and fit MHRV. Is there not a small void above the ceiling, or is there enough height for a false ceiling, a) to give insulation and b) hide the ducting?
4. ASHP set to run 24/7. Get the UFH system balanced so that you don't need any zone valves or stats in every room. Neither of my systems had any. The flow in each loop was set to match the heat loss in heat room and achieve the desired temperature, since then not been touched. The heatpump has an outside thermometer and simply controls the flow temp to the entire UFH to control the house temp. NO internal stats are involved - simple, no valves or controls to go wrong.

Just my thoughts based on my experiences!

Roger
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« Reply #11 on: November 21, 2020, 09:21:22 PM »

Why does everyone want to install heat pumps??   We do not have enough electricity generation to support this. Only last month major blackouts were narrowly avoided by firing up all our old coal power stations for a week. There is nothing "Green" about that.

https://www.theguardian.com/business/2020/oct/14/national-grid-warns-of-short-supply-of-electricity-over-next-few-days
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phoooby
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« Reply #12 on: November 22, 2020, 01:30:08 AM »

Quote
Why does everyone want to install heat pumps

On the assumption we need to stop burning gas so need to go to electric heating. 200-400% efficient heat pump beats 100% efficient panel heaters.

Maybe a case could be made financially for storage heaters (dirt cheap on ebay as no one wants them) coupled with small battery to cover 4-7pm for everything except heating. Switch to agile to get cheap leccy for all other times so you can run the storage heaters how you want them and cover 4-7pm with stored heat and use the battery for everything else so you don't get stung with 25-35p per kw leccy. 

I don't know what a 3-6 kw battery costs these days but with E7 heaters at about 30 each on ebay, the cost could be much less to install than a heat pump and UFH. Fit some smart controls to the storage heaters and battery to make the most out of the agile tariff and it may work out cheaper to run and cheaper/much less disruptive to install. Goes without saying that IWI would be needed to minimise energy usage.
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Mudman
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« Reply #13 on: November 22, 2020, 08:10:11 PM »

why install a heatpump? they seem to be the next thing... but i think that gas boilers may yet live to see another generation due to the chances that synthetic methane from excess cheap renewable electricity might feed the gas grid ... there's a good deal about this in the carbon commentary over the last year. would still have local air quality issues i guess from the boilers... anyway that's speculation for now.

Anyway, many thanks for all these replies, really interesting when you read the overall experience of people who've done years of this over several properties.
and the idea of getting a load of cheap storage heaters is interesting.

I guess if if was my flat and i had the capital i would do IWI, install a MVHR myself to do a careful job, and probably get someone to dig out the floor and insulate it to make the heat demand really low, probably installing pipes for heating and screed while i was about it. then i might do the storage heater idea for a year and see what that cost, using inline heaters for hot water. then decide if i had enough funds to get an ASHP or domestic battery (not a lot of space in the flat..).

Anyway, we'll see.

Any further thoughts on how to get tradespeople to actually fit IWI as carefully as is needed? And it seems it might need buildings control permission. anyone actually gone that route?



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kdmnx
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« Reply #14 on: November 22, 2020, 08:27:25 PM »

Round my way you can get the slab broken up, the slab and infill material removed, insulation installed and re-screened in a 3-bed semi for 4k. It is a standard job because thousands of post-war council houses used industrial waste as infill...

Obviously you have to be doing a total refurbishment and cannot be living there while it is done...
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