High humidity - new insulation or wet weather?

[Benjseb]

Hi all

 

We live in an old stone built house, which was renovated/insulated in 2005.

 

At the start of this year we had our internal upper floor ceilings (no loft) torn down, and 50mm celotex installed (gaps between rafters sealed with expanding foam) then reboarded and plastered. 

 

We also had about 5 new velux windows added and most internal walls skimmed.

 

A month ago downstairs we had the horrible plastic karndean pulled up and limestone tiles laid (with UFH + 25mm XPS insulation below). The concrete floor has a DPM and was dry to touch.

 

Previously our humidity levels were about 60-65% (expected to be a big higher as old house, no DPC). We'e noticed since about April (roughly when the ceiling work was finished) that our humidity levels have been above 70-75% on many days.

 

I'm fully aware that adding insulation/increasing air tightness can increase humidity,  but seeing as this house is probably fairly leaky, I didn't expect much of a shift when we did this. We've also added more ventilation from the velux vents. We have 3 decent DMEV trickle extractors which are running on boost mode 24/7 at the moment as the higher humidity levels are setting them off. 

 

As its summer, we often have the velux open (the velux are only even closed to 'ventilate' mode at worst, and often open all day).

 

As it's been quite wet here (North West UK) with the humidity levels outside often 80%+ I'm hoping this is just due to inside/outside temperatures being the same (or often lower inside due to the stone keeping it cool) and so the internal humidity being the same (or more) as outside

 

Do you think it could be the weather currently, or think we've created an issue with the work we've had done?

[Ferdinand]

Mine has been running at higher humidity than normal. I have been runnning my PIV a couple of settings higher.

 

I think it is too soon to conclude that you have a problem.

 

It may just be a combination of the extra sealing (even on an old house new ceilings throughout are significant - with the floor you may have lost 30% of your "leak ventilation"), plus all that grout etc under the new flooring will need time to dry out, and it can't go down 'cos you sealed that with Celotex. Suspect patience required for a couple more months as it aclimitises again. Plus new plaster is a good sealant.

 

3 suggestions that could help getting the background trend moving in a better direction.

 

1 - Set your trickle fans to the higher trickle setting if they have two (like my Vent-Axia ones do - 6 l/s and 9 l/s). The boost may also be adjustable with eg a rheostat on the PCB.

2 - Do the usual ventilation things when at home etc. 

3 - If you need you could try a dehumidifier. Domestic ones may help, but the one I swear by for leaks and rapid results is the Broughton CR40:

https://www.broughtoneap.co.uk/products/dehumidifiers/

Something to buy and sell, not rent except as a trial. Should get for ~£400 if you decide you need one. Small and needs a separate bucket, weighs about 26kg. Worth having the counter so your next purchaser can see it is mint. If dehumidifying, important to run the temp high in that area. Should have an impact on a normal sized whole house. Or get a decent domestic one and try it for a few days - will not hold its value as well.

 

Had I done that much to an old house, I would have a PIV as well as the trickle fans (normally do that in rentals) as a matter of routine, just for resilience and to keep air moving.

 

Remember that a newbuild takes about a year or two to dry out, so 4-6 months might be reasonable for all of that stuff you have done. I say do reasonable stuff to control it, watch, and wait until next spring/summer to take a check.

 

If you are measuring, a few of these min/max themometer-hygrometers might help see your swings. About £10 each.

https://www.amazon.co.uk/ETI-Ltd-thermometer-hygrometer-indication/dp/B017KNQNZA/

 

Ferdinand

Edited August 12, 2019 by Ferdinand

[ProDave]

I don't like to be a party pooper, but if you only have 25mm of XPS under your UFH you are going to be disappointed at the running costs as a LOT of your heat will be going downwards.

[Benjseb]

 

30 minutes ago, ProDave said:

I don't like to be a party pooper, but if you only have 25mm of XPS under your UFH you are going to be disappointed at the running costs as a LOT of your heat will be going downwards.

 

It’s a retrofit so all we could fit in. When I asked around quite a few people said it worked well, we will see!

[Benjseb]

1 hour ago, Ferdinand said:

Mine has been running at higher humidity than normal. I have been runnning my PIV a couple of settings higher.

 

I think it is too soon to conclude that you have a problem.

 

It may just be a combination of the extra sealing (even on an old house new ceilings throughout are significant - with the floor you may have lost 30% of your "leak ventilation"), plus all that grout etc under the new flooring will need time to dry out, and it can't go down 'cos you sealed that with Celotex. Suspect patience required for a couple more months as it aclimitises again. Plus new plaster is a good sealant.

 

3 suggestions that could help getting the background trend moving in a better direction.

 

1 - Set your trickle fans to the higher trickle setting if they have two (like my Vent-Axia ones do - 6 l/s and 9 l/s). The boost may also be adjustable with eg a rheostat on the PCB.

2 - Do the usual ventilation things when at home etc. 

3 - If you need you could try a dehumidifier. Domestic ones may help, but the one I swear by for leaks and rapid results is the Broughton CR40:

https://www.broughtoneap.co.uk/products/dehumidifiers/

Something to buy and sell, not rent except as a trial. Should get for ~£400 if you decide you need one. Small and needs a separate bucket, weighs about 26kg. Worth having the counter so your next purchaser can see it is mint. If dehumidifying, important to run the temp high in that area. Should have an impact on a normal sized whole house. Or get a decent domestic one and try it for a few days - will not hold its value as well.

 

Had I done that much to an old house, I would have a PIV as well as the trickle fans (normally do that in rentals) as a matter of routine, just for resilience and to keep air moving.

 

Remember that a newbuild takes about a year or two to dry out, so 4-6 months might be reasonable for all of that stuff you have done. I say do reasonable stuff to control it, watch, and wait until next spring/summer to take a check.

 

If you are measuring, a few of these min/max themometer-hygrometers might help see your swings. About £10 each.

https://www.amazon.co.uk/ETI-Ltd-thermometer-hygrometer-indication/dp/B017KNQNZA/

 

Ferdinand

 

Thats awesome thank you. 

 

Yes I guess that ceiling work and skimming probably has tightened things up quite a bit. We also had all new skirting that was foamed behind too

 

During the works we found our stove flue had been installed by a cowboy (there was a 6” gap!!) many years ago, so had to get that replaced so not had the wood burner working which is great at reducing levels of humidity. That’s now sorted as of last week so may crank that up to pull some air through the house and dry things off first and see how we get on. 

 

I’m really keen to make the air quality as good as possible as I have a tendency for allergies. PIV has been on my list, it’s a big house (250sqm) so think we may need two but unfortunately no loft so will have to try and use something like the Nuaire FlatMaster and box it in. A pain as well have to drill some big holes in the external wall. 

 

Thats put my mind at rest a bit so thanks. 

Edited August 12, 2019 by Benjseb

[SteamyTea]

Down here, in Cornwall, the RH has been high. Can always tell by how quick the freezers ice up.

[Ferdinand]

31 minutes ago, Benjseb said:

 

 

It’s a retrofit so all we could fit in. When I asked around quite a few people said it worked well, we will see!

 

it may well be better, but you may run into a constraint in the capacity of ufh if your walls are not insulated well.

 

The next step to have an eye on could be skirt insulation with eps in French drains round your house perimeter, but unlikely to be viable unless you are doing other groundworks such as eg replacing paths. Unless you have a minidigger and a lazy couple of weeks.

 

Ferdinand

Edited August 12, 2019 by Ferdinand

[Jeremy Harris]

20 minutes ago, Benjseb said:

 

 

It’s a retrofit so all we could fit in. When I asked around quite a few people said it worked well, we will see!

 

 

25mm of XPS underneath UFH will give a floor U value of around 1.2 W/m².K, so with the floor surface at, say, 26°C, a room temperature of 21°C and an underfloor ground temperature of 8°C then the heat loss into the ground will be about 42%.  26°C is not a particularly high floor temperature for UFH, either.  It equates to a power output, for the conditions above, of about 52 W/m². 

[SteamyTea]

13 minutes ago, JSHarris said:

52 W/m².

40 higher than my heat load.

[Ferdinand]

Quote

m really keen to make the air quality as good as possible as I have a tendency for allergies. PIV has been on my list, it’s a big house (250sqm) so think we may need two but unfortunately no loft so will have to try and use something like the Nuaire FlatMaster and box it in. A pain as well have to drill some big holes in the external wall.

 

I have a horribly complex room in roof setup, and my Nuaire Drimaster something something is installed in the toblerone space, entering the landing through the wall. Through the wall is iirc in a FAQ somewhere as OK.

 

It is in a sealed in compartment inside the space made out of Celotex, and is supposed to draw its air through the roof. I suspect that to finish this off it will require a ventilation tile connecting from the outside due to the membranes as much of the air may be recycled from room leakage etc  .. a little similarly to the way flues can go out through the roof. I think the bits are all available.

 

I do not see why similar will not work for you. But access for filters etc will matter for you.

 

I have the hall control version .. buttons under the cover ... but the remote and perhaps monitored version may be worthwhile.

 

F

 

 

 

 

 

 

 

[Jeremy Harris]

1 minute ago, SteamyTea said:

40 higher than my heat load.

 

Have to add another ~22 W/m² to that figure for the heat wasted in warming the ground under the house, too, so the true heat input (what's actually being paid for) will be around 74 W/m².

[Ferdinand]

Need to ask the painful question. How much insulation in your downstairs outside walls, if any?

 

What is the typical u value of such?

Edited August 12, 2019 by Ferdinand

[Benjseb]

7 minutes ago, JSHarris said:

 

Have to add another ~22 W/m² to that figure for the heat wasted in warming the ground under the house, too, so the true heat input (what's actually being paid for) will be around 74 W/m².

 

Not sure I’m following the figures completely. There no doubt would have been heat loss if we’d not added any insulation at all... Even without the UFH on there’s a noticeable difference now with the insulation under the tiles, maybe just because there’s less of a thermal bridge. 

[Benjseb]

2 minutes ago, Ferdinand said:

Need to ask the painful question. How much insulation in your downstairs outside walls, if any?

 

What is the typical u value of such?

 

Its stone built so no external insulation possible

 

walls are 600mm sandstone, cavity, brick inner leaf then either 50mm or 150mm internal celotex/EPS depending upon which room. 

[Onoff]

20 minutes ago, JSHarris said:

 

 

25mm of XPS underneath UFH will give a floor U value of around 1.2 W/m².K, so with the floor surface at, say, 26°C, a room temperature of 21°C and an underfloor ground temperature of 8°C then the heat loss into the ground will be about 42%.  26°C is not a particularly high floor temperature for UFH, either.  It equates to a power output, for the conditions above, of about 52 W/m². 

 

Funnily enough a mate of a mate, wanting to do similar as my bathroom thinks I've gone OTT putting 150mm pir + 25mm eps in my floor. He's planning "50mm eps then 2" screed with UFH". Aside from the heat losses I told him the screed is too thin.

[Benjseb]

Love the way you’ve done that Ferdinand. We literally have no voids though. It’s wall then roof so the only way to make that work would be to add a false ceiling and go out of the roof, but if doing that we may as well just go out the wall and box it in somewhere discreet. 

[Benjseb]

@JSHarris the specs for the XPS are:

 

Thermal Conductivity: 0.033W/mK

[Benjseb]

9 minutes ago, Ferdinand said:

?

 

What is the typical u value of such?

 

Approx 0.6 according to a heat loss calc we had done for heating system. 

[Jeremy Harris]

1 minute ago, Benjseb said:

 

Not sure I’m following the figures completely. There no doubt would have been heat loss if we’d not added any insulation at all... Even without the UFH on there’s a noticeable difference now with the insulation under the tiles, maybe just because there’s less of a thermal bridge. 

 

 

The issue is the much greater heat loss as a consequence of directly heating the floor to provide heating, so raising its temperature relative to the room.  This significantly increases the heat loss.

 

For example, if the house did not have UFH, then the floor surface would be a degree or two cooler than the room temperature, due to the heat lost through the very thin layer of insulation.  Assuming that the floor surface (without UFH) was 2°C cooler than the room temperature, so 19°C for the example quoted previously, then the heat loss would only be around 13 W/m² rather than about 22 W/m². 

 

Increasing the temperature of the floor temperature, by fitting UFH, always increases the heat loss to the ground, hence the need to fit a decent layer of insulation underneath it to reduce the loss and so increase the efficiency of the heating system.

[Ferdinand]

2 minutes ago, Benjseb said:

 

Its stone built so no external insulation possible

 

walls are 600mm sandstone, cavity, brick inner leaf then either 50mm or 150mm internal celotex/EPS depending upon which room. 

 

Better news.

 

Since you know a lot about your house, why not get the Jeremy Thermal Spreadsheet and build a decent thermal model of it? Then you will know where you are.

 

JSH will need to post a link, as it is currently not linked from his blog afaics.

http://www.mayfly.eu/2017/02/downloads-from-the-top-menu/#more-802

 

Just now, Benjseb said:

Love the way you’ve done that Ferdinand. We literally have no voids though. It’s wall then roof so the only way to make that work would be to add a false ceiling and go out of the roof, but if doing that we may as well just go out the wall and box it in somewhere discreet. 

 

Not quite as planned as it looks.

 

The place where the ventilation tile needs to go currently has 28 solar panels on it !

 

It is doable but intricate, which is why it has not happened yet.

 

F

 

 

[Jeremy Harris]

19 minutes ago, Benjseb said:

@JSHarris the specs for the XPS are:

 

Thermal Conductivity: 0.033W/mK

 

 

I used a λ of 0.034 W/m.K for the XPS, not knowing the exact product you used, and assumed that the underlying concrete floor was 100mm thick.  Using a λ of 0.033 W/m.K gives a floor U value (as far as the UFH is concerned - there will be no surface thermal resistance to account for on the top surface for this condition and the underlying ground will be in close thermal contact with the underside of the concrete floor) of about 1.19 W/m².K, pretty close to the figure I used.

[Benjseb]

25 minutes ago, JSHarris said:

 

 

The issue is the much greater heat loss as a consequence of directly heating the floor to provide heating, so raising its temperature relative to the room.  This significantly increases the heat loss.

 

For example, if the house did not have UFH, then the floor surface would be a degree or two cooler than the room temperature, due to the heat lost through the very thin layer of insulation.  Assuming that the floor surface (without UFH) was 2°C cooler than the room temperature, so 19°C for the example quoted previously, then the heat loss would only be around 13 W/m² rather than about 22 W/m². 

 

Increasing the temperature of the floor temperature, by fitting UFH, always increases the heat loss to the ground, hence the need to fit a decent layer of insulation underneath it to reduce the loss and so increase the efficiency of the heating system.

 

Understood. We only heat two rooms with UFH, kitchen/hall so these tend to stay at 18c on the stat - so yes, the floor temp will obviously be higher than that, but we're not using it in rooms where we hike the stat up high. Much of it was for comfort as the floor felt cold with Amtico so we were worried that with limestone it'd feel colder. It's much better now, but haven't had a winter yet to test the full effects. 

 

We actually still have all the radiators on the wall in those rooms which had already been oversized, so I'm hoping to use all in combination so we can run things at a lower water temp on the UFH.

 

 

Edited August 12, 2019 by Benjseb

[Jeremy Harris]

9 minutes ago, Benjseb said:

 

Understood. We only heat two rooms with UFH, kitchen/hall so these tend to stay at 18c on the stat - so yes, the floor temp will obviously be higher than that, but we're not using it in rooms where we hike the stat up high. We actually still have all the radiators on the wall in those rooms which had already been oversized, so I'm hoping to use all in combination so we can run things at a lower water temp on the UFH.

 

 

 

That's OK, it's just that some seem unaware that UFH is always less efficient, and wastes more heat, than any heating system that doesn't directly heat an external surface.  It's also quite limited in terms of heat output, as the heat losses to the ground rise dramatically as the floor surface temperature increases, plus there's an upper limit on heat output imposed by the maximum floor surface temperature that can be achieved.  This tends to be a particular issue with older houses, that often have a high heating requirement, and has led to some finding that UFH just cannot keep their house warm.  Not something you want to find out after having had it fitted.

 

We have 300mm of high density EPS underfloor insulation (λ = 0.034 W/m.K) and yet we still waste ~8% of the heat that we put in to the heating system, because of the losses down through the insulation to the ground beneath.  If we had radiators fitted to internal walls then our heating bill would be around 8% less every year.  We happily pay this premium for the comfort and convenience of having UFH, accepting that it's less efficient than some other forms of heating.

[Benjseb]

Good to know, thank you!

We're looking at getting an ASHP to replace an old knackered oil boiler. All the heat loss calls add up, but adding UFH was also a way of increasing the emitter size so we could run the water temp lower. Combining 45m2 of UFH with 5 rads should hopefully achieve this, and we can then play with the mix between UFH and Rads if needs be.

 

I'm hoping that the ASHP being on 24/7 rather than the up/down of oil will also help in our old building and stabilise humidity, etc due to less temp fluctuations.

[Benjseb]

Has anyone experiences with the Nuaire FlatMaster (or similar?) as I’ve seen lots of reviews of the Drimaster but not sure how the FlatMaster performs?