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How to improve cavity brick thermal performance?

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Started 11 years ago by munter
Latest reply from GBD

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munter
Member

Our double brick home is proving to be a challenge to heat through winter. The double brick walls have a relatively poor R value and the their high thermal mass takes considerable energy to bring them up to temperature. North facing windows are limited in number meaning limited passive gain. This ins't likely to change significantly as part of our upcoming renovations because of council's aesthetic requirements. The external walls are painted brick and the internal faces are rendered and painted. The house is in northern Sydney, about 8 kilometers inland. My question is - what can I do to improve the thermal performance of the existing double brick walls? Browsing the web turns up a few options but they all have their issues:

Hydrophobic fibre blow in fill - apparently reasonably common but some people claim moisture transfer is a problem from the external wall to the internal wall
Hydrophobic polystyrene ball fill - not a lot of examples around - is moisture transfer an issue?
Retrofit foilboard - difficult, fiddly and won't get in underneath window sills
External clad in rendered polystyrene - architecturally problematic as the house has only small eaves and centimeters of polystyrene added to the outside could start to look funny

A more off the wall idea I had was to consider some form of internal cladding for some areas. There is plenty of thermal mass in the solid brick internal walls anyway so could I isolate the living space in cold rooms with external walls by putting a layer of polystyrene on the internal face of the external wall? Could I even build in a bookshelf in front for extra insulation? Would condensation be a problem between the cold wall and the polystyrene insulation?

What would people recommend for this problem? What works? What doesn't? It must be a common problem as there are many cavity brick houses out there.

Posted Monday 23 Aug 2010 @ 2:23:39 am from IP #
cool at home
Member

Is it really 'off the wall' to clad some internal walls?? I'd have thought lining perhaps 3 walls of your coldest rooms would allow you to use both a plasterboard-type product with thermal properties, plus a thin insulation product like Aircell.

Posted Monday 23 Aug 2010 @ 3:59:35 am from IP #
dave lawrence
Member

moisture/condensation transfer is indeed an issue . cavity walls were initially conceived to defeat that age old problem. retrofitting cavity walls is a great idea in theory but in practice pretty difficult to achieve without compromising the moisture abatement.
can you extend your eaves and then batten out and insulate the outer skin of bricks. yes i know it is expensive but do you want good long lasting job ? failing that yes why not try cladding some internal walls in one room and monitoring the results .

Posted Monday 23 Aug 2010 @ 5:20:45 am from IP #
matas
Member

Its just a bit too difficult to retro insulate a brick cavity IMHO.
I emphasise with you, because I also have a double brick house on the North Shore of Sydney, thats cold in winter.
They say that most heat escapes through windows, then roofs, then floors, then lastly walls (I think).
So if you insulate your roof, floor and windows well, it shouldn't be too bad, in Sydney's mild climate.
Also, would it help to stop any drafts or too much air flow in the brick cavity ?
You could do this by blocking all openings into the cavity.

Posted Monday 23 Aug 2010 @ 6:11:57 am from IP #
dave lawrence
Member

do not block openings into cavity's ,they have another name "weep holes" ,they are meant to be there to let moisture weep out .

Posted Monday 23 Aug 2010 @ 6:14:03 am from IP #
dave lawrence
Member

all matas other ideas were good though. also as i sure you know pelmeted lined curtains etc and draft stoppers on doors and windows

Posted Monday 23 Aug 2010 @ 6:15:32 am from IP #
munter
Member

Thanks for the suggestions. I'm across most of the energy efficiency stuff like gap sealing and pelmets but really want to address the problem with the walls. Iincidentally, I have already sealed up the internal vents but the cavity is still well ventilated because there are ground level vents on the external wall and the cavity is open all along the top. I understood the internal vents to have been put there to deal with noxious gasses out of the old combustion heater which has since been removed.

I'm leaning towards some kind of internal lining at this stage. It would seem to be relatively simple (everything seems simple at first!), cost effective and with a low likelihood of water ingress problems. The disadvantage of losing the thermal mass isn't too bad when you think about the general excess of thermal mass that exists throughout the building. I've read on UK websites that this sort of approach get lead to condensation forming on the cold brickwork behind the lining but this may not be such a problem here in Sydney where it doesn't get quite as cold or as wet as the UK. Perhaps a 2cm thick sheet of polystyrene with a layer of plasterboard over the top would be enough on the southern wall? Given the uncertainty around whether this would work I think I might try it in one room to begin with before doing it in other rooms just in case it doesn't work or somehow fails.

btw - I think conventional wisdom is that uninsulated walls are a greater source of heat loss than uninsulated floors. Certainly there is a larger temperature gradient across the top of the wall than there is across the floor. We have a suspended timber floor which is now (mostly) insulated with R1.5 poly batts strung up with packing strapping.

Posted Monday 23 Aug 2010 @ 7:18:10 am from IP #
dave lawrence
Member

yes heat rises , thus greater losses up high than down low.

Posted Monday 23 Aug 2010 @ 11:26:26 am from IP #
GBD
Member

One issue with lining the internal walls is you are basically taking away the thermal mass by lining and insulating it inside -

The best solution is to insulate the cavity so you then retain the thermal mass of the bricks inside and insulate them from the outside temps.

As far as I know there is only one product suitable for this task - Moisture resistant rock-wool that is pumped in.

This product is treated and tested for it's moisture resistance to ensure it does not wick moisture between the outside wet wall to the inside wall.

It's also ideal for insulating cavity brick veneer homes.

You'll find some info here on the gains which are quite significant.

http://www.heat.net.au/action-advice-page

Click on cavity wall insulation sheet.

Posted Monday 23 Aug 2010 @ 7:13:21 pm from IP #
matas
Member

Cavity brick walls have high thermal mass, but without insulation are usually too cold in winter, and often too hot in summer if exposed to prolonged heat wave conditions. If the cavity is insulated, the internal thermal mass (ie. the internal brick skin) is protected from external temperature changes, and becomes highly effective at regulating temperatures within the home.

Insulate existing cavities by sealing the bottom of the cavity if it is open to the subfloor, and pumping in loose bulk material to a measured density. This has been common practice in the UK and Europe for many years, and is becoming available in Australia, usually in one of the following forms:

Small polystyrene balls (produced with CO2) coated in a non-toxic bonding agent are pumped in at regular points around the building. The bonding agent solidifies and locks all the balls in place.
Mineral fibres can be blown into the cavity either through a series of small holes as above, or into the top of the cavity if it is accessible. This material is gypsum isover mineral wool, commonly known as Isowool, and is moisture repellent, keeping the cavity dry.

http://www.yourhome.gov.au/technical/fs47.html#retrofits

(Sorry to just copy and paste a slab of text, but it did seem relevant)

Posted Tuesday 24 Aug 2010 @ 12:02:24 am from IP #
Eskimoau
Member

I'm not sure the internal thermal mass is that problematic. Yes, you do use a bit of energy 'charging' the walls but the trade-off is heat comes out over a longer period. I'm in Victoria and my place has solid internal walls with no passive solar heat gain due to a verandah aroudn teh entire house. We are comfortable heating to house to 19.5 degrees in the evenings and the temperature never gets below 17 degrees in the morning, so its's relatively efficient at retaining heat.

The Your Home Technical Manual (http://www.yourhome.gov.au/technical/fs47.html) outlines where you are likely to lose heat. Assuming you have adequate ceiling insulation, you can almost lose as much heat from windows, air leaks and floors as you do from the walls. Working on doing the cheapest things first perhaps you should look at whether there are any air leaks from doors or windows (door sausages are very cheap) or whether you could install better curtains in key rooms. If you're not built on a slab, you can also get underfloor insulation that you can install yourself. All of these would be cheaper options to investigate before starting on the walls.

Posted Tuesday 24 Aug 2010 @ 1:19:42 am from IP #
munter
Member

Thanks - I appreciate the additional advice. For the rooms in question we already have full length heavy curtains over the windows, the gaps around any external doors have been sealed and windows and the floor is carpet covered and insulated with R1.5 batts underneath. There is also R3.0 insulation in the ceiling.

For comparison to Eskimoau's results, when we heat to 19 or 20 degrees in an evening, the internal temperature can fall to 15 or 14 by the next morning even though I suspect we are in a warmer climate.

The house is quite old and the windows are quite small which is one of the reasons I am focussing on the thermal performance of the walls. Some form of mineral wool injection is looking like it might work. I'm a little concerned about moisture wicking across the walls though. Would a new external rendered finish over the current painted brickwork help reduce the chances of water ingress from the outside?

Posted Tuesday 24 Aug 2010 @ 2:40:56 am from IP #
matas
Member

I personally would never render and paint a good old face brick wall.
All that expense and additional future mainenance, and it doesn't look as good.
Like you are trying to hide crappy bricks or cracks.
Also, maybe it is somehow beneficial for the outer brick skin to breath.
I can't see moisture wicking being that great a problem, but why not choose a waterpoof filling, like polystyrene balls.
Also I believe you can get polyeurathane insulation foam that is pumped and expands, then sets.
Maybe that could be used.
Something like
http://www.total-insulation.com.au/spray_foam_insulation.php
or
http://www.ecofoamwallinsulation.com.au/
I would prefer a material that sets rigid, and doesn't settle over time, and is waterproof.

Posted Tuesday 24 Aug 2010 @ 3:01:47 am from IP #
munter
Member

lol - I am trying to hide crappy bricks and brickwork! The mortar is inconsistent and the alignment of the bricks is poor. The surface is also already painted so I am having to deal with the maintenance requirements of a painted surface already.

Posted Tuesday 24 Aug 2010 @ 6:37:37 am from IP #
dave lawrence
Member

1. if you are going to render over cavity brickwork , then IMHO you should NEVER paint it ,that way you NEVER need to " MAINTAIN" it .
2. Once brickwork is painted , you cannot apply a cementious render over it and expect it to stick . Acrylic render maybe ,BUT NOT OLD fashioned render .
3. Old fashioned render ( ie NOT the modern acrylic renders ) is only recommended on cavity wall systems ,because they still breathe allowing the bricks to dry out .
4. acrylic renders lock the moisture in .
5. I am talking from 15 years experience in a wet climate .
6. Although the other comments above may be true in regard to thermal insulation properties of cavity wall systems they completely ignore the issue I raised re : weepholes and the reason for the cavity in the first place .
7. As important as insulation is and a knowledge of issues around heat transfer etc. sound building knowledge and an understanding of different wall systems is vital for the health of the building . ignore it at your peril .

8. Once the bricks have already been painted ,unless you sandblast it off you ARE LOCKED into a maintenance regime .
9. NEXT consider a "rainscreen wall " . google it and read about it.

Posted Tuesday 24 Aug 2010 @ 6:49:21 am from IP #
Benny
Member

To some extent I agree with you Munter. IF you need to heat a room/house AND IF it has a lot of thermal mass AND if that thermal mass doesn't get any free energy pumped in to it (from N facing windows etc) then I can't see the advantage in having that thermal mass. OK it "smooths out thermal variations" but whats the point of that ? If you have a heating system running on a thermostat then all it means is the heater will come on for longer (to heat up the room as well as the walls) and then be off for longer (because the walls will release some of their energy as the room air cools down). If you don't have a lot of thermal mass, the heater will cycle with a shorter time constant. I don't see that it makes much difference just because "you can have the heater on in the evening then turn it off and the room is still warm in the morning". Why not just leave the heater on all night ? The amount of energy required to maintain the room air at required temp will be the same.
The critical issue as you raised is the insulation (R value) of the walls. If you are heating up the walls as well as the room air/contents then some of the energy put in to the wall is going to leak out as well as some leaking back in as the room air cools. If you have to heat a room then in my opinion the most important factor is to have very well insulated walls and thermal mass doesn't give you any advantage in terms of energy use. All it does (in the best case - say if there is good insulation in the cavity) is change the time constant - as you say it takes ages to get the rooms warm once they are cold. If I was going to put in insulation I'd take your approach and put it on the internal surfaces. Just heat up the things you need to heat and nothing else.

Posted Tuesday 24 Aug 2010 @ 7:45:04 am from IP #
matas
Member

I have to agree that thermal mass isn't too good in winter, unless it is warmed by winter sun, or a fire (ie. a chimney)

One minor thing, but the reason why I would not fill my brick cavity with insulation.
Is that I have electrical wiring in the cavities.
And I added more wiring, to the originals.
It would be totally impossible to add any more, in the future, with a filled cavity.

Also I can now shine a torch down the cavity, to check for termites.

Posted Tuesday 24 Aug 2010 @ 11:20:41 am from IP #
dymonite69
Member

Just a note on how cavities offer moisture control.

- bricks are porous (soak one in a bucket of water and weigh it!)
- rain moistens bricks or moisture leaks around fenestrations (e.g. window and door frames)
- sun comes out and heats the wall
- moisture is driven inwards (from hot outer surface to cold inner surface)
- moisture can either condense on inner surface or continues to vapourise into the cavity
- vapour strikes cold timber frame or inner brick wall and condenses
- condensation drips down in the cavity and leaks out weep holes.

If moisture is retained within the cavity it can cause rotting (structural failure) or mould (compromising air quality).

Various vapour/moisture barriers can be applied to prevent moisture entering the structural elements of the building. It is possible to build with no cavity as long as you can guarantee that moisture won't accumulate there.

Posted Tuesday 24 Aug 2010 @ 11:47:14 am from IP #
GBD
Member

The rockwool mentioned above is regularly sent away for testing to ensure it doesn't wick moisture - ie it's designed for the job.
As for polystyrene and expanded foam - studies are now finding that the expanded stuff in NZ is shrinking and the thermal performance is now way lower than it's original installation. Having personal experience with these foams in another environment I'm not surprised.
Yes filling the cavities has it's issues of cables, inspection etc.

Lining the walls is certainly an option - but it's also a pretty major job cost and disruption wise - ie light switches and power points moved, new cornices, window sills, architraves skirting board etc all needs to be ripped out, replaced or adjusted etc.

All depends on the budget and your desires as to what solution will best meet your needs.

Posted Tuesday 24 Aug 2010 @ 12:19:24 pm from IP #
matas
Member

GBD writes
"As for polystyrene and expanded foam - studies are now finding that the expanded stuff in NZ is shrinking and the thermal performance is now way lower than it's original installation"

Any chance of getting link/s or titles of these studies ?
Its just that I would be very interested to read them.

Posted Tuesday 24 Aug 2010 @ 11:17:14 pm from IP #
dave lawrence
Member

GBD writes
"As for polystyrene and expanded foam - studies are now finding that the expanded stuff in NZ is shrinking and the thermal performance is now way lower than it's original installation"
all building materials, including the way they react to moisture and temperature change though time ... which is why you are better off to rely on inbuilt design features (cavity and weep holes) than untested (through time) new products.
Which remind me ,none of the SIPS advocates have addressed my repeated questions about making changes to openings in the future . remember when we design a building we should not only be thinking of design in space (3 dimensions) but through Time , the 4th dimension .
Magazine architecture is rarely designed with time in mind .. it is by its nature static, designed for that snapshot ,but rarely with how it will behave in the future in mind .

Posted Tuesday 24 Aug 2010 @ 11:50:50 pm from IP #
ievans
Member

We've had roof insulation and window insulation/reflection (blinds/film) for a few years but found our brick veneer home still had only average thermal performance, especially during cold winter nights (heat loss) and the western sun during summer (heat gain).

We're about to have http://www.ecofoamwallinsulation.com.au/ installed into our 2 story home. I'll post an update once finished.

Some of the outcomes of my research to date:
1. The HEAT team were great for advice, even though I'm in NSW they put me onto some NSW installers.
2. The only internal insulation products that would meet my requirements were blown rockwool or expanding foam.
3. Ideally I would have had the insulation installed from the outside via holes drilled in the brick mortar. Unfortunately our steep slope and lack of external parking made this infeasible and costly (renting scaffolding etc). This means installing through holes drilled in the internal gyprock that will need patching.

Posted Wednesday 25 Aug 2010 @ 12:10:24 am from IP #
solar_star
Member

20 years ago I had rockwool insulation put into the cavity walls ( brick outer, breeze block inner) of my house in Europe. Took about a day. The house had already been rendered and they had a pig of a job matching the render colour when they painted over the drill holes. You could walk around the estate of houses and see who'd been "done" and who hadn't.

Being paranoid I calculated the volume of the cavity and used the quoted density figures for the fill to work out approximately how many bags they would require to fill the cavity. I then counted the bags as they loaded them into the machine - as it would have been almost impossible to tell whether they only part filled the cavity or not. To do the job properly the manufacturer set guidelines about how far apart the holes had to be to ensure the cavity was filled.

Now with infrared meters which can measure the temperature of different surfaces it would be easier to find the "cold" spots and get them back to do the job properly.

It did make a difference to how comfortable the house was afterwards.

Posted Wednesday 25 Aug 2010 @ 3:13:09 am from IP #
dymonite69
Member

If SIPS are like LEGO blocks why don't you just remove one or few to make a new door, window or connection.

Posted Wednesday 25 Aug 2010 @ 5:49:56 am from IP #
dave lawrence
Member

great idea, anybody done that ?
did it work ?
does it not restrict opening size to lego blocks ?
would you then design rooms around placement of said lego blocks ?

Posted Wednesday 25 Aug 2010 @ 6:19:29 am from IP #
Buzzman
Member

Sounds like munter's house is a typical post-Federation/California bungalow??? Most post-WWII houses are brick veneer, not double-brick (most..)

Seems like the problem is only a winter heating problem, rather than a summer cooling problem - ergo, the walls and insulation are doing a good job keeping heat OUT but so good a job that little is getting IN during winter to heat up the mass of the internal skin.

So adding to that thermal mass will probably not do a lot for the internal temperature in winter unless munter can also bring in more heat.....eith via larger windows or perhaps skylights designed to throw light (and warmth) onto the walls rather than the floor.

Generally speaking (and their are a lot of qualifications and conditionals) but generally speaking properly engineered skylights will be cheaper to install and let in more light and heat than a similar sized window.

Advantages
- easier and cheaper to install
- can direct light/heat onto walls

Disadvantages
- unless you place a false ceiling in the opening, they will let in a lot of heat in summer too

I used to see quite a few of these skylights installed on the North Shore when I ran a building maintenance business there back in the 80's - they were very de rigeur as well - and I can vouch for the difference it makes to a cold room or a cold house in winter.

The key is to position the the skylight in such a way that the internal shuttering (the 'tube' that leads down to the ceiling) is aimed at an internal wall so that heat can be absorbed.

Requires good architect or good research into sun angles, and may require tree pruning etc etc.

Another issue to be aware of.....if the house falls from 20 deg c down to 14 deg C overnight once heating is turned off as mentioned....this is quite normal and should not be a concern.

But my point is to get one of those internal/external weather stations and measure and record what the DIFFERENCE is between inside and outside. You might be surprised.

And as for Benny's comment about leaving the heating on so that the house stays warm all night....??? Uh, uh. No way.

Not unless you want a massive heating bill. It's far better and more cost-effective to cope with the diurnal difference (just like grandpa and grandma did, you bunch of wusses) and set the heating to come back on 15mins before your alarm clock goes off.

BUT, having said that, as an energy assessor I have to tell you that if you are heating any room that no-one is in or using you ARE wasting energy unnecessarily.

So from a "your personal environment and comfort" perspective, I'd advise the timer on the heater.

From an "eco-friendly energy-saving cost-effective sustainable future" perspective, I'd advise you to get a fleece jumper and tough it out.

It works for me!

Posted Wednesday 25 Aug 2010 @ 7:02:31 am from IP #
matas
Member

Buzzman
"I'd advise you to get a fleece jumper and tough it out. :)
It works for me! "
I couldn't agree more - a few jumpers, track suits and dressing gowns are pretty cheap effective insulation.
Its not like coastal Sydney is like Siberia or even Northen Europe.

I am just concerned Munter will spend many thousands on insulating his walls, only to find his house still chilly on winter mornings (maybe only a degree or so warmer).
Maybe its just inevitable on a winter morning, without a lot of artificial heating.

Posted Wednesday 25 Aug 2010 @ 8:11:04 am from IP #
dymonite69
Member

Nothing wrong with designing rooms the size of LEGO blocks. And if you can't find small blocks to fill the gaps then use something else. Don't have to be a purist.

Posted Wednesday 25 Aug 2010 @ 8:26:09 am from IP #
petacat
Member

have you thought about putting on external insulation?

You can get very good insulation that way and keep the thermal mass inside where is it useful. Several manufacturers are making this product that use expanded plastics, natural fibres and recycled waste materials - your preferences. The resulting wall can be rendered and or painted quite easily.

I did this on a West facing brick wall and the results were spectacularly good.

Posted Wednesday 25 Aug 2010 @ 8:44:22 am from IP #
Spud100
Member

We have a double brick downstairs and brick veneer upstairs house in North Rocks.
Hot box upstairs in summer and cold downstairs in winter.

Went to a company in Rydalmere run by 2 South Africans.
They do an injection foam system into the cavity.
They injected at the junction point between 3 bricks as we were rendering afterwards.
We chose the same system as we did in our previous house in the UK about 25 years ago and that my father did on a house that we built in Southern England 48 years ago.

Difference afterwards is that our heating bills went down over 20%.
On a very hot day before i.e. over 42°C the A/C could not keep pace.
Now we can keep the house cool with only 2 of the 3 systems on, and they are relatively ticking over. In the brick veneer area we now have around 125 mm of foam insulation. Also noticeably quietens the brick veneer inside.

However, overall we are very well insulated compared to the typical Australian hot box.
Double glazing, abour R5 in the roof, and whirly birds.
Gerry

Posted Wednesday 25 Aug 2010 @ 9:01:22 am from IP #

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