Hot lofts in Summer months........

I'd have thought it would be ok to have a loft full of hot air - you're protected from it down below by the insulation, and it's only the top of the rooms below that will be affected. It's more of an issue that hot air collects at the top of rooms and has nowhere to go.

It does help to make a convection cell where the hot air trapped in the upstairs can escape into the loft, and the hotter loft air can escape outside. But once you have some loft ventilation you can do that just by opening the loft hatch so the upstairs air can travel upwards and displace loft air which leaves via the vents.

I think convection should handle that without needing fans. It's only if you want to push that air downwards (eg towards soffit vents) do you need fans. Or if the vents are insufficiently sized.

Not the same setup, but in a loft conversion I have the option of closing the windows and trapping the solar gain and risen heat from the floor below, or opening the windows and allowing the air out, even though it's baking hot outside. The latter is cooler.

I think it would help, but you need to consider moisture control carefully. If the loft is warmer in the winter it's also damper, and it needs careful design to ensure the timbers get enough ventilation to dry out and not rot. If you went with fully insulated rafters (either insulation under the tiles or with eaves to ridge ventilation flow, insulation inboard of that, and a fully conditioned loft that would be one idea. But you really need to think about vapour control when doing so - a halfway house might be warm enough to be moist.

(My usual tool is to go to

Another option is solar panels. They offer shading which would reduce the amount of sunlight hitting the roof, and they turn about 20% of it into electricity. Once you've paid for the scaffolding the panels themselves are so cheap nowadays that if you can find a cheap mounting system you could consider them for shading first and electricity second.

Theo

In a sense I've gone the other way, using the excess heat in the loft as a convection engine to cool down the house core. A number of wedges in the uppermost overlap of the sarking sheets to open up an air path to the tiles and hence outside. Summertime replacing the wooden loft hatch with expanded metal sheet. Monitoring the outdoors shade temperature and the house core temperature , and when colder outside ,night time mainly, opening a small ground floor window with its own expanded metal sheet, as anti-burglar and anti-bug measure. Along with African sail shades raised over the outside of windows to prevent solar gain, works very well. Not the nonsense advice to close curtains to prevent solar heat gain, you want the " curtain" heat absorbing function on the outside of the glass, where that heat gain cannot penetrate the glass by radition or convestion

It's sensible advice - if you've exhausted other options.

It's much better to keep shading outside, but that assumes you have access to the outaide to install shading. If you're on the first floor or above (eg live in a flat) that may not be possible. We don't tend to have external shutters in the UK, sadly, and our use of overhangs is woeful (something the Africans do understand).

Curtains and blinds trap heat next to the glass and reduce hot air mixing with the rest of the room. Yes ypu get some mixing, so it's much worse than putting shading outside (even simple tinfoil on the outside is better). But some of the heat from the hot glass will radiate outside rather than coming in.

ie if all you have is curtains, it's better to shut them than leave them open. It coats you nothing to do, unlike installing proper shading.

Theo

Canopies work well if you can fit them.

They must work, as they aren't subsidised.

And open the windows to let the (very) hot air out?

Yes, if they open. At least when they are getting the sun.

Theo

For first floor windows, I have a pair of dinghy pulleys fixed above the window and a couple of loops of cord down to low level cleats, hopefully the cord is weak enough to break if a wind gets up.

Agreed, if you can rig up an awning that's a relatively cheap way to go. Wind loading is a problem though - you have to remember to bring it in when the wind gets up (or some of the electrical ones have a wind sensor and will stow themselves away).

Unfortunately continental shutters tend to require windows that open inward, which we as a rule Don't Do. Replacing your windows is an expensive affair and could mess with your internal layout (eg block a doorway or passageway).

Shutters with louvres are best because when closed they allow air flow with the inner window open, while keeping the sun out. Alas our window designs get so much of this wrong.

Theo

AIUI the old sash windows - gap at top and bottom - were ideally designed to allow passive cooling to work.

Again, no subsidies in that. Using centuries tried and tested designs is so ... well last century.

That is what we do, close vertical blinds, on the sunny side of the house, it certainly makes a huge, and very noticeable difference. We keep windows, and doors fully closed during the day, just one door open, fitted with a fly screen - I hate flys in the house. The blinds, prevent the solar gain landing on furniture and floors, to reradiate into the room.

Once the outdoor temperature falls, on an evening, we fling upstairs windows wide, to vent the heat stored in the fabric of the house, when there are no insects about.

Stand fans help in flushing out the hot air, especially if there's no natural cross-flow of ventilation.

Theo

I lived in Missouri for a year, and it got hot in summer. The house was fitted with a Whole House Fan, which sat in the loft, and when turned on when returning from a trip, it sucked cold air at a great rate from the cool basement up through the house, thereby cooling the house down. Opening windows provided more distributed cold air entry. It had intake vanes that were normally closed, but the airflow opened them. You had to have ear defenders handy, but, boy, it worked. The roof was fitted with two vents that rotated automatically with heat flow, and when this fan was running, they looked as though they would take off.

Last heatwave we kept curtains closed on the East and South facing windows. There is a storm porch that acts as a canopy over the rest of the South facing side of the house.

Then windows and front and patio doors open which created a gentle cross draught that met in the centre of the house.

It wasn't perfect, but very cheap.

One of the newspapers this summer suggested something similar ...

(1) Open uppermost windows (or your proposed loft extractor fans) to let out hot air that had risen in the house.

(2) Open ground floor patio doors and throw a bucket of water onto the patio. This is supposed to make the outdoor air drawn into the house cooler by a few degrees due to evaporating the water it passes over.

I have no idea how effective this is in practice.

My grandparents in Sicily used to sluice the pavement in front of their house. It seemed to work. (Their entire front was a set of "round the corner doors" they would open at 7 and leave them all day with dangly ribbons fluttering and sit and watch the world go (slowly) by.

I did contemplate fitting a Velux style loft window with an auto-vent giving the benefit of cooling in the summer and daylight, and longer views.

However that is ell down the list at the moment.

Cheers

Dave R

I wonder if London will ever adopt the Paris policy of sending bowsers of water around the city , early mornings , settling the dust at least and maybe cooling things down a bit for a while.

One of the streets in Cambridge has wide channels down each side, which act as gutters most of the year but were originally the public water supply and are fed from a local spring. When it's hot the spring tap is turned on and it does help to reduce the temperatures:

Far too sane