Home Repair & Remodelling

[Irfan]

Hi,
Some one told me that white wash is also a good insulator for roof. If a layer of Calcium Carbonate is quoted over roof then it will reflect the sun rays. In this way heat will not effect the interior of house. is it correct or not because it sounds very easy and could be done with a very light budget.

[Sammy555]

Hmmm. Well, speaking as a physicist, I can say that a white roof will absorb less light and should be cooler than a dark roof. The word "insulation" isn't the right term for this, though, since you're not really insulating the roof but simply changing the color to absorb less light. Also, keep in mind that there's generally an attic with a ventilated air space between your roof and the ceiling to your house, so heat isn't directly conducted from your roof to the rest of your house, There is, or should be, quite a bit of attic insulation between them, so I'm not sure how much practical effect cooling the roof will have on the house's interior temperature. But, yeah, as far as the roof itself a white color should keep it cooler than a dark color. A mirror reflective finish to the roof would keep it even cooler if you're willing to go that far.

[JimR]

While it would be "easy" to do, it wouldn't last very long.  One good  rain storm and your Calcium Carbonate is going to wash away.  Traditional white wash on fencing and such requires yearly reapplication and that's on a vertical surface.  People used it because it was cheap (much cheaper than paint) but it never was considered "quality".

Samy's comment is on point.  A white roof would have higher reflectivity than most other colors.  That's why there are white rubber roofing materials, white elastomeric coatings and white asphalt shingles.

[SCGUY]

But I would pay money to get neighbors reaction while watching it being applied.

[Irfan]

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Sammy555 wrote:
Hmmm. Well, speaking as a physicist, I can say that a white roof will absorb less light and should be cooler than a dark roof. The word "insulation" isn't the right term for this, though, since you're not really insulating the roof but simply changing the color to absorb less light. Also, keep in mind that there's generally an attic with a ventilated air space between your roof and the ceiling to your house, so heat isn't directly conducted from your roof to the rest of your house, There is, or should be, quite a bit of attic insulation between them, so I'm not sure how much practical effect cooling the roof will have on the house's interior temperature. But, yeah, as far as the roof itself a white color should keep it cooler than a dark color. A mirror reflective finish to the roof would keep it even cooler if you're willing to go that far.

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Yes word "Insulation" is not appropriate but fits good for my purpose. Keeping the mixture left for few days before applying increases its bonding strength. Its not my wording some one told me about it. He asked me to keep Calcium in Water for a week increses its strength. I would like to take your opinion on this as a Physicist. Secondly there is no ventilated air space between the roof and ceiling. Roof is just RCC. Therefore I have to use insulator or weather protection shield type solution but with low budget.

[El_Katz]

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Irfan wrote:

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Sammy555 wrote:
Hmmm. Well, speaking as a physicist, I can say that a white roof will absorb less light and should be cooler than a dark roof. The word "insulation" isn't the right term for this, though, since you're not really insulating the roof but simply changing the color to absorb less light. Also, keep in mind that there's generally an attic with a ventilated air space between your roof and the ceiling to your house, so heat isn't directly conducted from your roof to the rest of your house, There is, or should be, quite a bit of attic insulation between them, so I'm not sure how much practical effect cooling the roof will have on the house's interior temperature. But, yeah, as far as the roof itself a white color should keep it cooler than a dark color. A mirror reflective finish to the roof would keep it even cooler if you're willing to go that far.

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Yes word "Insulation" is not appropriate but fits good for my purpose. Keeping the mixture left for few days before applying increases its bonding strength. Its not my wording some one told me about it. He asked me to keep Calcium in Water for a week increses its strength. I would like to take your opinion on this as a Physicist. Secondly there is no ventilated air space between the roof and ceiling. Roof is just RCC. Therefore I have to use insulator or weather protection shield type solution but with low budget.

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Have you considered an elastomeric coating?  It is available in white. 

http://henry.com/roofing/coolroofcoatings/whiteroofcoatings/587whiteroofcoating

[Irfan]

No it was not in my mind and i am also not familiar with elastomeric coating.