Shade the original roof with a second roof : is that a good idea?

[HarrySeaman]

Dazuboz gave you good advice on how to aim the solar panels for maximum efficiency. 

 

I think solar cells are a great idea but before investing in the you need to do a careful cost/benefit analysis.  How much electrical generation from solar cells will you need?  Will you have storage batteries and if so what is the proper amount needed for storage?  Will you be able to sell excess electricity you generate back to the local electrical authority?  Will the reduction in your purchased electricity reduce your electric bill sufficiently to pay for the solar cells?

 

millymoopoo gave you and excellent list of how to reduce heating.

 

I'll add a bit of information.

 

The area beneath any roof will get hot when the sun shines on it.

 

If you put on insulated roofing you will reduce this heating a small amount.  It is probably not worth the cost.

 

If you put in the types of ventilation millymoopoo describes you will reduce the temperature of the area between your ceiling and the roof more than the reduction from insulating the roofing. 

 

If you then put in insulation on the ceiling, with a heat reflective layer on top of this insulation, this will reduce the amount of heat that can transfer from the space between the ceiling and the roof into your living quarters. 

 

The combination of improved ventilation between the ceiling and the roof and insulation on top of the ceiling is best.

 

Another thing that will help is to reduce the amount of sunlight that is absorbed by your roof.  Using two layers of roofing with ventilation between the layers, as you are proposing, is one solution.  Another solution is to use a white roof instead of a colored roof.  Heat reflecting white paint for roofing, etc. is sold in Thailand.  It is expensive and will need to be renewed occasionally but I know from experience that it works.

[digger70]

18 hours ago, gejohesch said:

Is it realistic or far-fetched?

It's really doable and it works, In Aus many people used that idea on mobile homes /caravans in the tropics .

Edited June 29, 2021 by digger70

[MarleyMarl]

I did this recently, who would think you need to build a roof, over your roof? I had it built mostly to stop leaking, but it has also helped with heat.

 

I recommend to use the metal sheets with the reflective insulation under. I didn't use it because I have good insulation under the main roof, and I was told because my new roof is exposed it could peal off.

 

My townhouses have a pretty poor designed roof, and when it rained on certain angles, water would get under the tiles, through the skylights, and ruin all my brand new gyprock ceilings inside.

 

Edit: I got the idea from my neighbors several units down, you can see their roof in the distance. However for mine I used galvanized steel and more posts. It's pretty sturdy.

 

 

Edited June 29, 2021 by MarleyMarl

[gejohesch]

8 hours ago, Crossy said:

I would be tempted to take the steel support columns down to ground level unless you are certain of the existing structure.

Good point. Thanks

[gejohesch]

5 hours ago, Dazinoz said:

Agree about the pitch. Not sure where the OP is located but the ideal siting of solar panels in Chiang Mai is facing due south at an angle of 18.7 degrees with out shading. Panels should be pitched at the same angle of the latitude where they are placed. As i said in CM need to be 18.7 degrees and mine in Brisbane, Australia were at 27 degrees facing north.

I'm near Khon Kaen, say 16 degrees latitude. I'm aware of the ideal pitch for the panels. The issue with the roof I am talking about is that it is pitching due east / due west. Hence the idea of building a small horizontal platform on top of the house: the solar panels can then be mounted on that platform and ideally pitched towards the south.

[gejohesch]

5 hours ago, ICELANDMAN said:

 

The practical demonstration of how to do the difficult things when you can do the simple things.

 

Laying a single metal roof with insulation has not yet come to your mind?

Of course, and that's part of the plan. But why add other heat insulation devices if that does not come too expensive?

[ICELANDMAN]

2 hours ago, gejohesch said:

Of course, and that's part of the plan. But why add other heat insulation devices if that does not come too expensive?

 

Because it is cheaper to make only one insulated roof than to make two roofs. The solution of two roofs is made when on the first flat roof where you can walk you can make a terrace and take the breeze of the wind under the protection of the second roof. But in your case it is a waste of time and money even if you want to recover the original roof sheets, if you also put a photovoltaic system it is better that it is as low as possible to access it in case of problems on your system.

 

[ICELANDMAN]

2 hours ago, gejohesch said:

Of course, and that's part of the plan. But why add other heat insulation devices if that does not come too expensive?

 

Another advantage to consider I am talking about aluminum sheets with insulation that is currently produced where I should no longer have to change them for life, they cost more but it is the quality that counts for a material on a house if you want not to have future problems.

 

[BritManToo]

Just now, ICELANDMAN said:

Another advantage to consider I am talking about aluminum sheets with insulation that is currently produced where I should no longer have to change them for life

Lots of these around me, usually the insulation is hanging off after a couple of years.

[ICELANDMAN]

9 minutes ago, BritManToo said:

Lots of these around me, usually the insulation is hanging off after a couple of years.

 

I do not know anyone you speak of, probably they have been glued on the under roof manually, these very recent ones of a few years are industrial products that have a thickness of 6 cm of insulation and more and being in aluminum they are indestructible with the weather, excluding typhoons.

 

[kokesaat]

I agree.  White metal roof with the thick foam lining on the underside of the roof (very common on new metal roofs now).  You could also add batts of insulation to your ceiling....cheap and effective.

 

[Dazinoz]

3 hours ago, gejohesch said:

I'm near Khon Kaen, say 16 degrees latitude. I'm aware of the ideal pitch for the panels. The issue with the roof I am talking about is that it is pitching due east / due west. Hence the idea of building a small horizontal platform on top of the house: the solar panels can then be mounted on that platform and ideally pitched towards the south.

Its good you are aware of ideal placing of solar panels, most people are not, even so called professional installers..

 

I put a 3kw system on my house in Australia about 12 years ago. Quite expensive then so i did a LOT of research before going ahead. After it was completed I would see new systems popping up everywhere and I would look at some of the placements of the panels and think to myself they have wasted so much money.

[gejohesch]

4 hours ago, ICELANDMAN said:

 

I do not know anyone you speak of, probably they have been glued on the under roof manually, these very recent ones of a few years are industrial products that have a thickness of 6 cm of insulation and more and being in aluminum they are indestructible with the weather, excluding typhoons.

 

Maybe I have not looked enough around. I could only find sheets with 5mm insulation glued underneath. It does not sound like the sort of material I should go for...

[gejohesch]

4 hours ago, Dazinoz said:

Its good you are aware of ideal placing of solar panels, most people are not, even so called professional installers..

It's not rocket science either, if you just look at the basic idea. As you say, a bit of reading is sufficient to understand how it all works. But maybe for some, understanding how the sun trajectory varies through the year is a bit too much!

 

In my case, I have modeled my 2-houses compound in Sketchup (to the nearest few cms accuracy) and referenced the model to the actual lat and long, plus correct orientation of course. With that done, I can play a lot with the sunshading option available in Sketchup. It's of great help to understand where and how I can add sunshading screens, for example.

[sometimewoodworker]

10 hours ago, gejohesch said:

Maybe I have not looked enough around. I could only find sheets with 5mm insulation glued underneath. It does not sound like the sort of material I should go for...

Probably not

[gejohesch]

5 hours ago, sometimewoodworker said:

Probably not

Any idea about the prices? Thanks!

[gejohesch]

20 hours ago, kokesaat said:

You could also add batts of insulation to your ceiling....cheap and effective

Insulation batts have been mentioned several times. Can someone give a few details, or summarise, on available options and costs per sq. m? I have just under 100 sq m to cover, but I'm also a bit concerned about the weight and how the ceiling can take it. The ceiling was installed during my absence, so I'm not sure how strong it really is...

[sometimewoodworker]

6 hours ago, gejohesch said:

Any idea about the prices? Thanks!

No but the address is http://www.siamthaisteel.co.th/index.php

[Sheryl]

I was able to substantially cool my house by doing the following when it came time to replace the roof:

 

1- installed radiant barrier (foil)

 

2- improved ventilation in the space between roof and ceiling (more windows and fenestrated fascia boards under the eaves)

 

3- used very white colored roof tiles for the new roof

 

4- installed awning to shade the windows

 

These measures together easily lowered indoor temp by about 5-10  degrees. 

[gejohesch]

3 hours ago, sometimewoodworker said:

No but the address is http://www.siamthaisteel.co.th/index.php

Thanks

[DiDiChok]

Goodness me!  I can't believe what I've been reading in this thread.  It's as though nobody has ever been up country in Thailand to see how the locals deal with this problem.  There is a really cheap and most effective solution that is more practical and quicker to install than all the other suggestions on here.  It's a roof for goodness' sake!

 

What you do is to install mini sprayers on the ridge line of the roof with a tap to control the water supply to a pump.  The locals often do this when next to a pond where they keep fish.  Some of the water trickling down the roof evaporates taking with it the heat, and the rest is collected in gutters and goes back on to the roof via the pump.

 

The roof loses a lot of heat and even more than a lot if there's any wind at all, the water gets aerated and when the water comes from a pool the fish don't seem to mind either.  Plus it's really cheap to run and lovely and cool underneath the roof.  Simples.

[GlennSN20U5]

On 6/29/2021 at 4:19 PM, BritManToo said:

Lots of these around me, usually the insulation is hanging off after a couple of years.

I think you are referring to what the local called it PE Insulation / Air Bubble Insulation. Yes, they do tear after few years. But he was referring to something superior which is PU Aluminum Foil Roof.

[GlennSN20U5]

On 6/29/2021 at 1:35 PM, gejohesch said:

Of course, and that's part of the plan. But why add other heat insulation devices if that does not come too expensive?

This heat insulation panel will be long term fix. Like one off installation.

I think you can search Re-Roof Service. A lot of local they did this to old tiles roof. Basically they add Tower Support & C-Purlin Bar over the old roof then insulation (EPS,PU or Rockwool) foil and metal sheet roof panel over it. It is easy and very light. Provided your old existing roof are in good shape and condition. 

I think this will be cheaper than steel structure and cement roof. If you intended to go for Solar Panel eventually, I reckon to go for Standing seam roof so that your solar panel can mount easily. No bolt, less leakage in the future. Best of luck.