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Black roofs in MMGW summers?

Nimby

Distinguished Member
There is a craze over here in Denmark for replacing roofs with black concrete tiles (or even worse) glazed black clay tiles. The latter use much greater quantities of energy to produce compared with conventional clay roofing tiles.

Meanwhile I have been examining roofing materials which do not soak up the sun's rays.

So I had a tour round a couple of builders merchants touching displays of roofing materials with my fingertips in hot sunshine. My unsophisticated tests suggested that white pigmented, corrugated, fiber-reinforced concrete sheets are always cold to the touch. (Note: Not the cheapest uncoloured sheets which quickly discolour from original white to grey)

Most other roof covering materials were all far too hot to touch regardless of colour or the material used. I would probably have needed a digital meat thermometer to measure their temperature!

Downside? Not many people like white corrugated roofs except avant-garde architects building modern houses. Flat sheets are available in tile form but are much more expensive. These look rather like white slates set on the diagonal in use.

No amount of batt insulation will keep out the sun's heat in summer. The roof covering heats up to tremendously high temperatures and radiates straight through the insulation into the rooms within. Perhaps not a problem if the roof isn't occupied but a nuisance if it is. It would be nice if the roof surface could be "switched" to match the seasons but this is completely impractical in most cases.

Hot roofs must add to the heat island effect of tarmac roads and carparks.
Anything which reduces their absorption and re-radiation should be beneficial.

Conventional pitched roofs don't lend themselves well to "living" turf roofs.

White tarpaulins are unsightly and very prone to wind problems and rapid UV breakdown.

I considered greenhouse white-out wash for the summer season. But wondered whether it would discolour the roof permanently leaving the house potentially too ugly to be sold. The wash might not work on absorbent roof materials anyway.

Thatch is a wonderful material but far too costly for most homeowners.

Any thoughts?
 

johntheexpat

Distinguished Member
I don't know if you have come across this in the bacon factory, but its all the rave down in the wine cellar. A 17 layer roll like this is supposed to be way better than 150mm of rockwool, keeping heat in during winter and keeping heat out in summer. Being thin, you can staple it to the batons in your roof, so installation is easy. It's not that cheap, but compared to others it is good value and the ease of installation makes for a lot. The only real precaution is that you should still allow the roof to 'breath' properly, but as it is stapled to the batons that is usually the cause by default.


http://www.castorama.fr/store/Catal...p-categorie_6816-casto_product-PRDm527058.htm
 

Nimby

Distinguished Member
I think I'll have to work out the cost of covering the rafters in cooking foil.

It would cheaper than applying gold leaf to the roof surface. :)

Cooking foil won't make the roof cooler but it should reflect some of the radiant heat.

The layered stuff looks a bit too expensive but would only need to be used on the southern side.

Covering the roof in solar panels would be another way of reducing heating of the roof surface.
 
J

jackal

Guest
My house has a double roof This type of shape: ^^ roofed in stone which unfortunately soaks up a lot of heat.

I am probably going to go down the solar panel route for the inner V (if you get what I mean), but it is so hard to get any meaningful information about what grants etc are available to help share the cost.

Also the one company I asked for a quote wouldn't do so because the of the roof material (old stone slabs as I mentioned) and other safety related issues.

Can anyone point me in the direction of some good companies in this field and national guidelines on planning and grants.
 

Corey USA

Established Member
What of painting the roofs white to reflect heat back up as ice does. You would probably need some kind of crystal based paint since the idea is to bounce heat back to space.. Or if there was a way to apply Prisms to a surface to mimic ice crystals.
Foil covered house? be sure to have the sunglasses on. :devil:

reality is, we need trees close to the house which may be the long term solution. Yes we have the risk of the trees falling on the house but is it an acceptable risk vs the alternative of climate chaos?

In areas that trees won't survive due to poor planing by leaders we will have to find alternatives.

If we can't remove the heat then we need to use it. maybe the thermal heating for water? only problem is the limited amount of hot water available since it takes time to heat it. but what of using it in conjunction with on demand water heater.(not the old style water tank) you could feed the water from the thermal heater on the roof through it and the on demand water heater would only heat it as much as the increase needed based on the starting temp of the water.

The thermal water heating unit also acts like a radiator to a certain point. In that when the water is in use new cool water is introduced to cool the whole system down to a certain extent until the sun heats it back up again.

Jackal Are you within city limits? If not you may have to locate a "do it yourself group." It may not be insurable in this manor though. The reason for do it yourself is that you can jury rig something that works. Great rewards comes with great effort. Meaning the solution is not going to be easy.

Also you may want to look into "thin film" solar which reduces the weight big time in theory in that you don't have all the excess weight from heavy silicon and its support framing. Weight is the primary safety issue on your particular roof.

http://www.powerfilmsolar.com/products/building_integrated/membrane-roofing.html
http://www.powerfilmsolar.com/technology/index.htm

http://www.aip.org/tip/INPHFA/vol-9/iss-2/p16.html
 

Nimby

Distinguished Member
There used to be a water heating roof which had open corrugations of metal sheet. A spray bar poured water down the corrugations from the ridge. It heated up on its way down and was collected in a gutter, filtered and brought into an insulated tank indoors. From whence it was pumped round again. Downsides were evaporative loses and birds droppings contaminating the roof. A more sophisticated version has a glass cover over the corrugated sheets. Cost must have been high with the glass covered version.

Regarding Jackal's plea for a company to supply the kit I cannot help. I do worry though about shading of the solar panels by the other roof of the inverted "W" at any other time but midday in high summer. The sun only rises to about 10 degrees above the horizon in midwinter at the top of its curve through the sky seen from the UK.
 

Corey USA

Established Member

Nimby

Distinguished Member
From memory, any concentrating passive solar collector is poor in cloudy situations. The conventional solar collector can go on collecting at a lower rate. Off axis solar collection might also be down on normal passive. Driven solar collectors, which follow the sun, are a possibility but need much more space, complication in support and are unsuited to pitched roof mounting. They may also be subject to wind damage and planning permission. Clear ground with a clear view of the Southern sky is necessary. No shade can be allowed from trees, bushes or buildings over a wide arc and the plumbing is inevitably longer and subject to heat losses. In comparison a south-facing pitched roof with conventional passive solar absorbers may be slightly less efficient but is much easier to arrange and is much less likely to suffer from shading.
 

Corey USA

Established Member
What I was reading about the holo version is it improved its efficiency over previous versions of Pv solar.
 
J

jackal

Guest
Regarding Jackal's plea for a company to supply the kit I cannot help. I do worry though about shading of the solar panels by the other roof of the inverted "W" at any other time but midday in high summer. The sun only rises to about 10 degrees above the horizon in midwinter at the top of its curve through the sky seen from the UK.

This is what I had thought about also. Unfortunately it is the only place where I could consider them. The house is 500+ years old and although not listed I'd never get it through planning.

I am also looking into turbines, but their cost and relatively low output (15KW is the highest I have seen) make them not particularly viable as yet.

Until they make these options more affordable and eaiser to get through planning, people will never see them as a viable alternative to the national grid.
 

Nimby

Distinguished Member
Placing the solar panels other than on the roof may be your only option.
Garage roofs are popular sites. Ye olde outhouse if no garages exist. :)
 
J

jackal

Guest
Plenty of out buildings, I'll makes some calls tomorrow and see if I can get another compny to take a look.

Cheers for the answers.
 

Nimby

Distinguished Member
Plenty of out buildings, I'll makes some calls tomorrow and see if I can get another compny to take a look.

Cheers for the answers.

Have a look at Velux Windows solar panels. They mix and match them with their skylights. No idea as to prices, quality or performance. Might suit a particular situation where a more traditional appearance is desirable.
 

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