Cool an attic during hot weather

Heating, insulation, ventilation, VMC, cooling ... short thermal comfort. Insulation, wood energy, heat pumps but also electricity, gas or oil, VMC ... Help in choosing and implementation, problem solving, optimization, tips and tricks ...
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gegyx
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Re: Cool an attic during hot weather




by gegyx » 23/05/22, 21:04

Thank you for your return.

But I have 3 small skylights that I open in the summer. But it's not at the highest point of the slope.
I just made a calculation, I must have 2.3 times more than 6 cat flaps for 90m2.

So no overpressure :D

Just a fiber cement slate roof, which has become Black with lichens and time.
Insulation between attic and living space with glass wool (and vapor barrier) that has lived...
And a lot of mess above which must store a lot of heat.

Ah! Under the glass wool there are 4 to 5 cm(?) "Stramit" slabs, an old ceiling finish, composed of agglomerated straw (or shavings?), but the binder is not cement.
and below a smooth cardboard finish, to be painted.
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Re: Cool an attic during hot weather




by gildas » 23/05/22, 21:42

gegyx wrote:Thank you for your return.

But I have 3 small skylights that I open in the summer. But it's not at the highest point of the slope.
I just made a calculation, I must have 2.3 times more than 6 cat flaps for 90m2.

So no overpressure :D


However, I think you need the same ventilation power on each side of the roof for a good draft (?): We have 3 ventilation tiles on each side at mid-height. (ordinary tile roof)

gegyx wrote:Just a fiber cement slate roof, which has become Black with lichens and time.
Insulation between attic and living space with glass wool (and vapor barrier) that has lived...
And a lot of mess above which must store a lot of heat.

We have a bit the same problem our glass wool is packed and old = Bad insulation..

They have it for 1€ they have isolated their height : Shock:
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Re: Cool an attic during hot weather




by gegyx » 23/05/22, 23:28

Yes, except that the floor boxes are more or less concealed with boards, furniture, boxes, boxes, well-stacked books and clothes and others... and I think there are quite a few mini volumes of insulation in all this bulk of a good height.
Removing, or moving all this, seems insurmountable to me. : Mrgreen:

And if lightning strikes in there, I think it will take a canadair! But I am in the center. : Wink:

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: Cheesy: The problem did not occur today. He fell from the ropes, and several times during the day...
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Re: Cool an attic during hot weather




by Obamot » 23/05/22, 23:49

I'll also respond with stuff I gleaned from another thread.

It would be well to already examine the points given by Gildas. (In particular renovating your thermal insulation with these state credits, if they still exist! Be careful to get yourself a very good mask, if you get rid of the old one, my biochem teacher did not hesitate to say that it was also toxic than asbestos... IMPERATIVE) : Idea:

Then:

Cool the roof with water — I'm not going to comment too much because I half believe it, but it is:
— either we aim for permanent cooling with a substantial volume of water but which is constantly renewed using a pump (still would have to find how to lower the temperature of the water after it has passed through the roof + store in a tank)
— either we aim for a minimalist solution which consists of making a mist that will evaporate instantly on touching the roof, and as this will create an exchange — it will extract heat from the roof. What is to be hoped for (but this is speculation) is that the mist created, behaves in its homogeneity like “a deflection of the sun's rays on the drops forming thermal insulation”... But as the contribution of the Sun is gigantic in comparison, I fear that the fogging will not be able to overcome the powerful Helios, The only way to measure its effectiveness is still to just do a test to see...! (Without any paraphernalia).

But anyway, for that you need large misting production units with large fans.

From experience, I think this will have little effect since your attic is already insulated and the heat automatically escapes through the top.

: Arrowd: This is what I would do in the absence of a complete ITE : Arrowd:

You have to take the house as a thermodynamic system with flow control.

Passive measures

Windows open or closed?
Open to the attic, and I would add large electric fans to evacuate the heat under the roof to the outside.

Closed or open controlled flow for below.

There you have 2 possibilities, you have to try both.
— either all the doors and windows are closed on the side of the facades exposed to the Sun, to prevent the temperature from rising through the windows, but there in the middle of summer, you can wait until 22 p.m. to see the temperature be bearable (sufficiently lowered) . Unless you create a draft effect (see below)
— either everything remains wide open on all sides to evacuate as much as possible, and come what may...

Venturi-like effect

2DBC8784-328F-40B0-8AF0-21BC3868DD1C.gif
2DBC8784-328F-40B0-8AF0-21BC3868DD1C.gif (34.22 Kio) Consulté 2188 fois


With an option of air circulating from the cellar, if you are lucky enough to have one with step-overs. In this case: everything is closed everywhere, except the accesses which give to the cellar, and a leap of wolf and a window on the floor opposite the course of the Sun) if possible in the bedroom if it is due north or to the east (and not if it is placed in the course of the Sun, south, southwest) in all the systems stated : Arrow: the optimum is found when the draft is the strongest (as in a fireplace)

If so, you take advantage of the temperature difference between the penultimate floor and the cellar, to use it like a “venturi effect” to circulate the air at high speed and cool the masonry during the day.

(it being understood that — with the exception of the “high wind” option where everything is permanently open — whichever option is chosen, all the windows facing the course of the Sun must never be open during the day, under any circumstances.)

It's up to you to know and understand how to control your entire system.

I come to the essential point, (and if you manage to do that, you will have won the game), you have to find a way so that the Sun does not hit the facades, that's what creates an effect of 'steamroom.

There are several ways to achieve this

We can for example put a hanging tarpaulin - it's not aesthetic but it's to show the idea - held by straps at the edge of the roof, if possible held firmly to the beams, and kept at a certain distance from the facade, Tarpaulins fixed with cables perpendicular to the ground, these passing through eyelets and holding on their own (the cable passing alternately through the eyelets on the inside then the outside.)

All this to prevent the Sun from hitting the masonry of the upper floor (where you want to sleep). Because it is easier to ensure that the temperature of the walls does not increase, than to cool them afterwards, which in the absence of a good ITE, is hardly possible.

a point of equilibrium must be found in this thermodynamic system, so that the temperature remains as low as possible, which means that everything must be optimized — and each time using as many combined techniques as possible — if not taken independently the gain is very weak.

The other way is to create on the first floor a 60cm sconce, or a small balcony, as follows:

CA3753B5-9447-4E78-AEBC-EA38B77C83B9.jpeg


I put 60 cm, because I don't know how much your roof protrudes from the facades, it could be 30 cm or whatever, but you have to be able to open and close the curtain.

Then just put a curtain on it

76F8F27A-A38A-4EF1-A7A0-D70A066D87CD.jpeg


And for the ground floor a blind that would go down as low as possible. but a curtain can also do the trick depending on the height of the ground floor.

I dismiss the 3rd possibility of ITE since you did not retain it.

Now if that's not possible, these are the basic reflexes:
— everything in the path of the Sun is permanently closed.
— anything opposite the path of the sun can be either open or closed (to allow air to circulate : Arrow: but inside from the basement. The goal in the latter case is to keep the cool inside as long as possible)

But in some houses, it is the “everything open everywhere” which gives the best result (you have to experiment.)

Active measures:
— maintain a body temperature that is as low and comfortable as possible
— so do not expose yourself unnecessarily to the Sun during the day
— hydrate regularly before having the evening, always have a glass of water on hand because the feeling of being thirsty decreases drastically with age.
— take regular showers to lower body temperature:
— eat cold, preferably fruit that lowers body temperature:
— put on fans, it lowers the body temperature and also the sensation of “felt heat” drops instantly. This is where I come back with misting, there are fans / misters.
— these ladies like to use a fan in the summer...
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Re: Cool an attic during hot weather




by izentrop » 24/05/22, 08:49

Gildas wrote:Seen by chance a construction pro and exposed the problem: You have to see if there are ventilation tiles on the roof... The problem of overheating can come from there if there are not enough or not enough... .
There are about 6 for 90m2 of surface... (ordinary tiled roof)
For the fibro slate (?):
https://www.cba-materiaux.fr/p/toiture- ... c-A3072122
It is more to protect the roof and the frame from summer overheating and winter condensation between the screen under the roof and the cover, in addition to high and low ventilation, in the event that it is insufficient. The comfort of the inhabitants depends rather on the quality and the quantity of the insulation.
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Re: Cool an attic during hot weather




by gildas » 24/05/22, 09:42

gegyx wrote:Yes, except that the floor boxes are more or less concealed with boards, furniture, boxes, boxes, well-stacked books and clothes and others... and I think there are quite a few mini volumes of insulation in all this bulk of a good height.
...


All of this mini volumes of insulation seems misleading to me: All this density of materials must conduct heat better than an insulation of 30cm or 40cm not packed...

So pretty much agree with Izy (despite the controversies on certain subjects).

Obamot wrote:I'll also respond with stuff I gleaned from another thread.

It would be well to already examine the points given by Gildas. (In particular renovating your thermal insulation with these state credits, if they still exist! Be careful to get yourself a very good mask, if you get rid of the old one, my biochem teacher did not hesitate to say that it was also toxic than asbestos... IMPERATIVE) : Idea:
Thank you for the advice, I always doubted when handling glass wool...
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Re: Cool an attic during hot weather




by Obamot » 24/05/22, 10:50

Very good reminder indeed, I had not evaluated this detail since — insulation, as its name suggests, must imperatively cover the surfaces from one side to the other, otherwise the heat exchanges (which take place whether we like it or not) : Lol: will be concentrated on the non-insulated areas, which can cause attacks / mold on the structures — this is why I also suggested reviewing all the thermal insulation on the ground, and putting cellulose wadding instead and place, rather... It smells like a garage sale in the air (which would sometimes be desirable as fire prevention...)
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Re: Cool an attic during hot weather




by Obamot » 24/05/22, 11:15

izentrop wrote:The comfort of the inhabitants depends rather on the quality and the quantity of the insulation.

Your example is a bit absurd, I apologize. If you talk about “comfort of the inhabitants” you don't need your sketch with all-out air circulation ... then you need under-roof thermal insulation that passives the house and therefore with a double flow VMC! Because your thing in the summer relieves a little of the heat, but in the winter it serves to cool the house in the worst possible way, since the heat loss is done from the top, the AC system literally sucks the heat produced in- below. So question “comfort“You will come back, your thing is only used in non-insulated dwellings. And Gégyx having chosen not to do any work (or a minimum) he is not going to correct his roof (he did not ask for it)

And that's where it hurts.
Your sketch contains errors, the airflows in blue are “under-roof” so they must be represented in dashed lines : Arrowd:

0F00F98F-9E75-450A-B277-E77EE7E8CC2C.jpeg
0F00F98F-9E75-450A-B277-E77EE7E8CC2C.jpeg (135.37 Kio) Consulté 2073 fois
the arrows — showing the evacuation of the air extracted from this “furnace” formed by the accumulation of heat under the roof at high temperature — must be in red.
...and the air is not there “RADIO” but de facto CONSTRAINED thermodynamically. More amateur rhetoric.
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Re: Cool an attic during hot weather




by izentrop » 24/05/22, 11:41

Gildas wrote:These mini volumes of insulation seem misleading to me: All this density of materials must conduct heat better than an insulation of 30cm or 40cm not packed...
and not ventilated... Just measure the temperature on the hot side and on the indoor side, excluding air circulation
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Re: Cool an attic during hot weather




by Obamot » 24/05/22, 11:43

izentrop wrote:
Gildas wrote:These mini volumes of insulation seem misleading to me: All this density of materials must conduct heat better than an insulation of 30cm or 40cm not packed...
and not ventilated... Just measure the temperature on the hot side and on the indoor side, excluding air circulation

You just expressed the opposite with your sketch, do you realize?
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