Of empty wall cavities and cavity insulation

[N_Cook]

Is cavity infill insulation counter-productive summertime.? I've recently commissioned easily removable (for non sunny days) "African" external sail sun shades for ground and upper floor, over the windows. I've been very impressed with the effect , since blocking solar gain through the windows, and keeping windows closed during the heat of the day. Even in the hottest day for centuries last month , the core of the house rose only 1 degree C above the early morning minimum temperature. This is an old terrace house with plain empty wall cavities. Would the situation be different if there was rockwool or fibre or foam insulation blocking the migration of any heat build up through the outer brick skin and no longer able to rise through the cavity into the loft?

[bert]

In article <tc8l8q$ukm9$ [e-mail], N_Cook [e-mail]> writes

It would seem so as there are no articles on just this effect on new build houses. We too experience it as we have had cavity wall foam for many years. Just can't cool the house in the evening. One useful tip is to open the trap door into the loft and the hot air rises. Surprising but true. I've now fitted an extractor fan on the landing to clear the hot air which gather at the top of the stairs.

[N_Cook]

A couple of years ago , for each summertime, I replaced the wood loft access pannel with metal mesh. At least the hot air does not descend. Checking with a joss stick, air vaguely enters the roof-heated hot loft with no windows open and vigorously enters with a downstairs window open, But only worth doing when the outside air is lower than the core house temperature, not during the day. I can tolerate the cold of our now warmer winters but not the heat of hotter summers. I think at this stage , I will stay with tradional open "flue" cavities. I might try a remote temperature sensor in the loft where the cavity emerges and one on the adjascent internal brickwork and see for myself what is going on

[Andrew]

Not surprising since warm/hot air expands and rises, so as long as you have some sort of ridge tile vent then the (even) hotter air in the loft will escape through this vent once the sun has gone down and the outside air cools and warmer air from the house rises into the loft to replace it. Also helps if you have open windows on the cooler side of the house to allow cooler air to replace what is rising up and being expelled.

I did wonder if painting my grey marley modern roof tiles with solar control paint (that silvery stuff) on the south flank would be beneficial. I might give it some more thought because my loft was up to 47C on Hot Tuesday.

[Brian]

We have cavity insulation - the house was built with it. Subjectively*, I would say it helps in the summer, as does the extra loft insulation, to keep the house cool. Our loft gets VERY hot and I added extra insulation after the first year or so. We noticed the upstairs was both cooler in summer and warmer in winter.

The design of our house is unusual, we have a large roof area, meaning it is prone to both heat loss and solar heating when the sun shines. It is detached, split level, with three floors, two at the back, one at the front. Modern double glazing etc.

• compared to other houses with empty cavities we’ve owned etc.

As a rough guide, even in mid winter, our heating is timer is set to go off at 8 pm. I normally set the temp to 20 C. We have a Hive system which sends me reports of the house temp. By 6:00 am or so, when the timer is set for, the temp has rarely dropped below 18 or so, even on cold nights. We like the house to be comfortable, we don’t sit a shiver, but not hot.

[Harry Bloomfield Esq]

+1 Very effective.

[N_Cook]

Its a shame thatched roofs are such a fire hazard and only last a few decades, they must be the best for keeping solar heating out and internal heat retained inside, ideal for both summer and winter

[The Natural Philosopher]

You can get glass fibre thatch

[Jamesy]

No.

But you might get a different result if it had lasted longer as it did in

1976 due to significant thermal inertia.

Can't see why it would given that the insulation would stop the heat getting to the inner skin.

[Jamesy]

It would be interersting to see if they are actually better than modern insulation.

[Brian]

Even a properly constructed pitched roof, with insulation under the tiles ( with vapour barrier/ ventilation etc) would probably be better than how we normally do it. Lofts would be more useful for storage etc., you could still insulate between them and rooms below, but they wouldn’t be subject to the extremes they are now.

[Vir Campestris]

In this hot weather our thatch was great at keeping the heat out. It stayed under 30 inside the house.

In winter.... well, I've been up in the loft on a windy day, and there's significant airflow in the loft. It doesn't seem very warm in winter.

OTOH our previous houses were all over 200 years more recent. It may well be something else keeping it cool in winter!

Andy

[N_Cook]

I did not like the idea of no trap, for fire propogation reasons. Whether correct thinking i've no idea. Summertime replacemet I use expanded \aluminium mesh ,my theory being its perhaps like Davey miner's lamps, keeps any flame on the flame side of the mesh and also steam train smokestack mesh function to reduce arson of farmer's fields. Also did not like the idea of mice abseiling into the house after climbing the cavities into the loft

[Brian Gaff]

Also a lot of terraced properties built in the 1930 to1960s had no cavity at all. Brian

[N_Cook]

No windproof sarking under a thatch roof?

[Vir Campestris]

Nope.

There's a thing called "The Dorset Model" which advises you on how to construct a _new_ thatched building, but old ones have to be kept as they always have been.

Andy

[N_Cook]

Interesting stuff on fire prevention. Years ago i was involved with civil-engineering/building materials. The dept did some research on an unusual fire source in thatch. The Wennington, outer London/Essex compost-heap initiated spontaneous combustion extensive fire last month reminded me of it. With a thatch in poor condition , ie rain ingress, ISTR by nesting birds pulling out strands, so not obvious from looking at the thatch. I suppose these days , even as a community purchase , if a number of such roofs , a scan by IR camera or even IR thermometer might show hotspots at night with no fires on inside the biulding to confuse things.