Internal Insulation for solid walls - a mini blog

RenovationMan

Our house has 400mm thick solid sandstone walls that we are looking to insulate. We're not allowed to insulate externally as the building is listed and we live in a conservation area. We are therefore forced to use internal insulation, which is a shame because we then face the problems of moisture in the walls and we lose the thermal mass of the sandstone.

To fix the first problem I have been looking at breathable insulation that will allow any moisture in the walls to pass through the insulation and into the house, to then be extracted via a Heat Recovery Ventilation system (TBA). After researching and subsequently discarding many products such as sheeps wool, hemp batts, etc. due to the thickness required to hit current building regulations, the expense and the hassle involved in their installation, we have found a breathable PUR board similar to celotex/kingspan boards but with evenly distributed holes filled with a vapour permable mineral.

The boards are called IQ Therm and manufactured by a German company called Remmers. The boards we will use are 80mm thick with a thermal conductivity of 0.031 W/mK. The boards are installed and then covered with the manufacturer's breathable render and painted with breathable paint. The render will have the same suface quality as the existing internal plasterwork and the manufacturer's breathable paint can be used on the IQ-Therm product, lime mortar and gypsum which means that we won't have to touch any of the internal dividing walls other than to give them a bit of a skim and paint them.

We are doing the house one room at a time, starting with what will be our eldest daughters bedroom. Aside from putting IQ-Therm on the external walls we will be putting insulated plaster panels on the ceiling for heat and sound insulation, on one dividing wall for the same reason, rockwool in the bedroom floor, lagging on the central heating pipes and fitting LED down lights lights, a new cast iron radiator and replacing the cold slate window sills with thick oak ones to reduce cold bridging.

I thought that a mini blog might prove interesting/useful to anyone who has a similar solid wall house and is considering improving its energy efficiency.

RenovationMan

Just to add, we have already made some efforts to improve the energy efficiency of our home by installing a 'warm roof' consisting of TLX Gold breathable multifoil insulation above the rafters (and below stone roof tiles), with a 25mm air gap and 50mm PUR (celotex) boards between the rafters and 75mm PUR (celotex) beneath the rafters. With plasterboard beneath that forming the vaulted ceiling for all of the top floor bedrooms. We are really happy with the result and have noticed that snow and frost now last forever on our roof.

We have also installed a thermal store that provides our hotwater and central heating requirements, driven from a gas condensing boiler and wood burning stove. The TS has a coil for solar thermal, but as yet we have not installed this (hassles with listed building officer).

Our intended aim is to have a character home that was built in the 18th century, but with 21st century levels of comfort and energy efficiency and the running costs of a modern home.

rogerblack

RenovationMan wrote: »

Our house has 400mm thick solid sandstone walls that we are looking to insulate.
<snip>
Snap!

To fix the first problem I have been looking at breathable insulation that will allow any moisture in the walls to pass through the insulation and into the house, to then be extracted via a Heat Recovery Ventilation system (TBA).

As I understand it.
The issue you may face is - in addition to dampness of the walls due to 'rising damp' (possibly not a real issue in your situation) and ingress of water due to weather - there is dampness due to water vapour from the habited volume going through your insulation.

The only way this will not happen will be if you are actively ventilating the wall structure, or have the inside quite dry indeed.
http://en.wikipedia.org/wiki/Dew_Point - see specifically the graph with straight lines.

If you have exterior walls at (say) 5C, and the internal temperature is 25C, then you need a humidity of under 25% or so in order for there not to be condensation on the insides of the (stone) walls.

This is quite dry, and will indeed need a reasonable amount of air exchange.

http://www.ewp.rpi.edu/hartford/~pastor/MEP/Other/References/Counter%20Flow%20Heat%20Exchanger.pdf - may be interesting.
DIY easy-to-construct heat exchanger.

http://www.metoffice.gov.uk/climate/uk/averages/ukmapavge.html - may also be of use.

bobhawke

I'll be following this thread, I have an old house with solid walls, high ceilings and terrible insulation.

RenovationMan

bobhawke wrote: »

I'll be following this thread, I have an old house with solid walls, high ceilings and terrible insulation.

I spent this weekend pulling down plaster from the ceiling and one wall that connects to the living room (we're putting soundproofing in both). I have a bit of lime pointing to complete here and there and while this dries out I'll do some remedial work while I have access, such as moving electrical sockets, etc.

I'll then be all set to 'dub out' the wall with hemp lime plaster to level it off prior to fitting on the insulation panels. I'm slightly worried about the plastering as I have never done a complete wall before, but I don't have to get it smooth (the rougher the better so that the insulation adhesive sticks), I just have to get it level. The good thing about lime is that it takes a good while to dry so I'll have plenty of opportunities to ge it level.

I'll post some pics once I've done the plastering.

whasup

I see no value in having breathable internal insulation. Internal vapour pressure is always higher than external so normal vapour migration is from inside to outside. It is true that this can reverse but only in exceptional circumstances and for temporary periods such that the effect can be ignored. This depends on having well designed external finishes - i.e. correct lime mortar joints and no vapour resistant renders etc - and normal protection from extreme water ingress. Given this and if your house has reasonable air flow around the external you will not cause problems by using a standard thermal laminate.

rogerblack

whasup wrote: »

I see no value in having breathable internal insulation. Internal vapour pressure is always higher than external so normal vapour migration is from inside to outside.

In the UK at least - other climates differ.
Indeed, there may be benefit to having some airspace, in place of the plaster, to allow air to circulate inside the wall structure somewhat.
You can level by 'dabs' of plaster or blocks of wood.

RenovationMan

whasup wrote: »

I see no value in having breathable internal insulation. Internal vapour pressure is always higher than external so normal vapour migration is from inside to outside. It is true that this can reverse but only in exceptional circumstances and for temporary periods such that the effect can be ignored. This depends on having well designed external finishes - i.e. correct lime mortar joints and no vapour resistant renders etc - and normal protection from extreme water ingress. Given this and if your house has reasonable air flow around the external you will not cause problems by using a standard thermal laminate.

There has been a huge amount of discussion around putting insulation into older houses that have solid walls and I've read articles that champion both sides of the debate and I have personally come to the conclusion that Breathable is the way to go for our home. Naturally, everyone should DYOR and come to their own conclusions.

I saw several articles that stated how difficult it was to prevent internal water moisture (condensation) going through the insulation and condensing on the cold walls behind, causing damp and the resultant mould growth and damage to stonework and especially beams/floor joints. The articles all stated that even with the vapour barriers on the back of celotex or Kingspan (the silvery material), taping the joints between abutted celotex boards and even adding a separate vapour control layer, moisture can get through over time as the seals deteriorate). Contrasted with this is breathable insulation that stops damp from being trapped behind the insulation (the insulation forms part of the wall) and allows any moisture in the walls to vent back into the room.

The information that really got me on board with breathable insulation was in "The Old House Handbook", which described how rising damp was caused in old houses by the application of a damp proof membrane and concrete slab into the ground floor, forcing ground moisture along the underside of the impermeable sheet and up into the walls.

It's a brilliant book and I highly recommend it to anyone who has an older house.

albyota

Very interesting blog RenovationMan, keep it up.

some good info here

http://www.historic-scotland.gov.uk/hstp102011-u-values-and-traditional-buildings.pdf

and here

http://www.historic-scotland.gov.uk/paul_baker_thermal_performance_of_traditional_masonry_walls.pdf

and for windows http://www.historic-scotland.gov.uk/thermal-windows.pdf

http://www.energy.salford.ac.uk/cms/resources/uploads/File/Retrofit%20Papers/035%20Rye.pdf

whasup

That's fine. It's for you to make your mind up. I speak from a great deal of (professional) experience in renovating and refurbishing period properties. Sadly, many of the people I meet in my professional capacity have learned most of what they know from books. I learned mine from hands on research and years of taking buildings apart and undoing the mistakes of 20, 30, 40 years ago - the cement years.

RenovationMan

albyota wrote: »

Very interesting blog RenovationMan, keep it up.

some good info here

http://www.historic-scotland.gov.uk/hstp102011-u-values-and-traditional-buildings.pdf

and here

http://www.historic-scotland.gov.uk/paul_baker_thermal_performance_of_traditional_masonry_walls.pdf

and for windows http://www.historic-scotland.gov.uk/thermal-windows.pdf

http://www.energy.salford.ac.uk/cms/resources/uploads/File/Retrofit%20Papers/035%20Rye.pdf

Thanks for those, I read through the first link in the list and found it really interesting and will read through the rest over the next few days.