Why does the house get so hot at night?

Our house is about 7 years old. Outer red brick walls, cavity insulation, aero type blocks for inner wall, dot and dab plasterboard finish.
By day the house is reasonably comfortable, save the conservatory. But as night comes the house starts to warm, especially upstairs making the smaller rooms really stuffy.
Anyone know why this is and how we might stop it?
We have added an extra layer of insulation in the loft but this has not helped much.
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On Sun, 08 Jul 2007 23:37:52 -0700 someone who may be garym999

For a full diagnosis the orientation of the house, shading and room layout would be needed.

It is probably simply the hot air rising over the day and you notice it when you go upstairs to bed (presuming the bedrooms are upstairs).
If it is then try opening some of the windows on the ground floor and top floor slightly during the day. Opening them wide is not necessary. This will produce a gentle current of air which will limit temperature rises. In particular try opening the windows on the shaded side of the ground floor and sunny side of the top floor. Obviously leave the internal doors open. This may be difficult if the house is unoccupied during the day, but opening them this way in the evening may help and you can experiment at the weekends.
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David Hansen, Edinburgh
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David Hansen coughed up some electrons that declared:

That is the conclusion I came to as well - my modern well insulated house is horrid by evening upstairs in summer.

My trick was to open all the upstairs windows wide as soon as I come in after work (or just after supper). By bedtime most of the stored heat has dissipated and the air is fresh again.
Unfortunately, my wife's hayfever has kicked up again, so it's back to being a steamed dumpling. I'll try your method next, David.
Cheers
Tim
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On Mon, 09 Jul 2007 10:38:17 +0100 someone who may be Tim

Insulation slows down heat coming in through the walls and ceiling and so contributes to keeping buildings cooler in summer.
However, it does not stop radiation through the windows and if there are large areas of unshaded southward facing glazing then the heat this produces will be slowed from escaping through the upstairs walls. The answer to this is to deal with the glazing, and/or limit the solar temperature rise by ventilating.
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David Hansen, Edinburgh
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On Sun, 08 Jul 2007 23:37:52 -0700, garym999 wrote:

Insulation keeps heat in... But I guess you close the windows at night even if they are open during the day. This will also trap any heat. As Mr Hansen says open windows a little low down on the N side and high up on the S. Draw the curtains on the south side during the day.
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Dave Liquorice wrote:

The key to keeping houses cool in summer is to SHUT the windows by day - and the curtains - and OPEN them at night.
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On Mon, 09 Jul 2007 10:20:08 +0100 someone who may be The Natural

If the windows don't allow much sunlight through. Otherwise the sensible approach is to limit the solar temperature rise by ventilation during the day. Cool air from the side of the building away from the sun should be let in at low level to get the maximum cooling.
Remember that sunlight falling on (internal) curtains will cause a temperature rise within the room.
At night the ground, warmed by the sun during the day, is giving off relatively hot air and it makes little sense to draw this into the building.
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David Hansen, Edinburgh
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David Hansen wrote:

Curtains are not noted for their inherent transparency.
Otherwise the

Not in this house,. With air temps up to 30C outside, and internals nearer 25C, we don;t want any of that outside air coming in thank you!
Cool air from the side of the building

No, in the space between the curtains and the windows.. you DO have insulating curtains I hope..

Not at 3.a.m. it ain't.
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The philosopher is right on this one. And it goes further too. If you vent the house all night long, the temp of the fabric of the building drops, (not the air temp, which is a different beast) and this reduces the daytime temp rise, as the brickwork starts off colder.
This can also be done effectively during the evening if (and only if) you use proper control system. Waving your hand out the window and saying which is warmer leads to a totally ineffective result.
A differential thermostat plus fan can thus be used to knock a few degrees off the house temp most of the time. Worked very well at last place.
Windows that lock in the open half an inch position can be useful for this.
Resulting hay fever can be dealt with by wet filtering the incoming air - but dont let the cloth dry out or the dust is released. Put it in the wm while wet..
NT
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On Mon, 09 Jul 2007 08:41:51 -0700 someone who may be snipped-for-privacy@care2.com wrote this:-

Incorrect.
It goes down because there is not a solar gain at night. The flow of heat in the fabric reverses. Ventilation will reduce the temperature of the fabric to some extent, but the extent of this depends on the conditions (including how much heat is being given off by the ground).
Of course what happens depends to a large extent on the particular sort of building one is considering.
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David Hansen, Edinburgh
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David Hansen wrote:

That radiates straight out. The ground surface is typically the coldest place at night - hence ground frost/mists etc.
Openimng low level windows is very effectice in intridiceing cold air and if teh upper windos are open too, a chimeny effect develops.

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I'm sure you understood what was said really.

bingo
yes, but most of us live in brick or block. Anyone living in a wooden shed is out of luck.
NT
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snipped-for-privacy@care2.com wrote:

Thats a good trick..

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...one thing i didnt mention before is it needs a lot of airflow for many hours, but given that it works nicely.
NT
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On Mon, 09 Jul 2007 14:51:42 +0100 someone who may be The Natural

They are however generally on the inside of the house. Sun hitting them will cause a temperature rise within the house.

You have the same external air temperature on all sides of the house? Fascinating, but unlikely this far away from the equator.

The air in that space is generally connected to the air in the rest of the room, whether the curtains are insulated or not. Do you have some particular arrangement of curtains where this is not the case? If so, what is it?
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David Hansen, Edinburgh
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David Hansen wrote:

Single glazed windows, and floor length interlined (3 layer) curtains: There is almost no air movement between the trapped space and the room.
The curtains/sg windows are in fact more effective than triple glazing.

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wrote:

*envy* How do you get the house so warm?
Does the conservatory act as a heater? Can you close the doors to it to prevent heat flowing into the house?
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The rear of the house, with the conservatory faces NNW. Of the four bedrooms one is to the rear, others to the front. The master bedroom windows are open all year and the radiator is never on.
Upstairs by day is fine. Early evening is OK but by late evening the difference is staggering. I know heat rises but I thought extra insulation in the loft would help prevent the build up in there. As we use the loft and it is boarded out I stapled Airtech to the joists. And that has knocked the temp in the loft down a lot.
"*envy* How do you get the house so warm?" Wish I knew. We brought the house off plan and I don't think it was built to any exacting standards, there are no cavity closures that I know of. If anything there is a draught blowing behing the dot and dab.
I have wondered about the conservatory build up as this does get real hot and as it is joined to the lounge you feel it in there too. but having the doors open lets it all blow away.
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But that would trap the heat underneath, where you don't like it ...
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It keeps the heat radiating from the hot loft.
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