House roof space

Hi,

it would just remove the heat radiation particularly under a roof and eventually at the back of a wall exposed directly to the sun.
Temperature wise it wont make much difference.

We have successfully installed foam insulation with a foil backing on the inside of a resto roof. Lowered the temps radiating from the roof significantly. I don't know the effectiveness if you only rolled it out in the attic though.

Ok thanks a lot for information scott

I havent tested, but I believe the difference between good and low results is if making so the hot air between the metal roof and the foil get made to move out.  It can be made WITHOUT fan if "correct" side are at the shade side and it can need a ventilation at the roof TOP leting the air out there.

SHADING by trees and/or e g by tarp at the sunny side when the sun start going down can make big diference too.
A  Swede built his living house and Filipinos a posh pig house       with vent leting out the heat at roof top and leting air in at bottom and insultion/shading made it much less hot. The Swede has AC but he need to use it very seldom.

Thanks for your reply Dave

Thanks for your reply Dave

Architecs here install foil insulation under the metal roof to keep the attic cool not realising that in so doing, the metal becomes hotter than design causing further expansion. The paint will crack aowing water ingress that will rust and shorten the life of the roof. Better to insulate the ceilings and have open gable ends for the hot air to escape. DESIGN the house for the hot air to dry the washing.

The contractor installed 25 mm double foil faced foam insulation under the roof panels of my new house. It is a new concept for me and I asked the foreman how it was supposed to work. I have he standing ridge metal panels and the foreman says there is air flow through the ridges. The house is a lot easier to cool than I imagined.  Like many Philippine houses my house has a hip roof so no gables to vent.

I installed ridge vents on the last two houses I owned in the US, one shingle roof in Houston, TX and one metal roof in south Georgia. I followed the ridge vent manufacturers recommendation and sealed off the gable end vents and installed or enlarged the soffit vents. Makes sense the the air flow through the ridge vent would follow the path of least resistance so if you pull in the air at the gable ends the air in the lower portion of the attic is stagnant. Better to pull the air in along the soffits and cool the entire roof like illustrated in the video.

https://www.youtube.com/watch?v=j57VpjoVngY

With the rolls of white foil backed insulation material in Ace hardware, they go to great lenghts to explain the installation method and that is the suspend the material along wires close to the metal roof surface with foil side upwards. This allows the hot air to move along the metal and result in cooling. The houses I've seen built here just trap the foil under the roof between the framework and with the foil side downwards.
I have a solar heating system here with a framework leading to a s/s tank where i run off the hot water.  To contain the hot water in inclement weather I wrapped the tank with one layer of insulation, this lasted 5 years and now needs replacing.  My frame of water pipes are set in strips of metal furongs ? and to improve the efficiency I cossetted them with strips of insulating material. However the weather has made them deteriorate and I sweep up bits from the garden. during the afternoon the sun goes down and cooler draughts will reduce my overall heat from the tank. however we shower at 4 pm if the weather cools off quick.

Moon Dog wrote:

Better to pull the air in along the soffits and cool the entire roof like illustrated in the video.

https://www.youtube.com/watch?v=j57VpjoVngY

Yes.  I have told some poor Filipinos in years now they can  improve their houses cheap even if just use scrap paper if they make so it become such air flow.  Old newspapers can insulate good, I mean compared to nothing. 

Peter Clark wrote:

With the rolls of white foil backed insulation material in Ace hardware, they go to great lenghts to explain the installation method and that is the suspend the material along wires close to the metal roof surface with foil side upwards. This allows the hot air to move along the metal and result in cooling. The houses I've seen built here just trap the foil under the roof between the framework and with the foil side downwards. .

Haha   Many Filipinos (malay) seem to like to do things backwards so it dont suprise me

coach53 wrote:

Moon Dog wrote:

Better to pull the air in along the soffits and cool the entire roof like illustrated in the video.

https://www.youtube.com/watch?v=j57VpjoVngY

Yes.  I have told some poor Filipinos in years now they can  improve their houses cheap even if just use scrap paper if they make so it become such air flow.  Old newspapers can insulate good, I mean compared to nothing. 

Peter Clark wrote:

With the rolls of white foil backed insulation material in Ace hardware, they go to great lenghts to explain the installation method and that is the suspend the material along wires close to the metal roof surface with foil side upwards. This allows the hot air to move along the metal and result in cooling. The houses I've seen built here just trap the foil under the roof between the framework and with the foil side downwards. .

Haha   Many Filipinos (malay) seem to like to do things backwards so it dont suprise me

Yup the bling2 (shiny silver side) must always be displayed for all to see....forget the reasoning.

To add to your inputs, my house is a "Hermoso" bungalow. I have taken out the decorative windows at both ends of the house and installed louvers, seems to cool the house a bit. Hindsight being 20/20 vision, l should have removed all of the roof and replaced it with a a single gable ventilated with louvers both ends and double sided insulation on the ceiling. I would change the roof colour to white from the heat attracting dark brown.  regards  Bruce

Our house was designed round the idea of cool air being drawn up into the roof space and vented. BUT because the rear of the house faces North, the winds enter the roof that way and blow hot air downwards into the bedrooms...drying the laundry on the way. The force of the northern winds is greater than scientific hot air rises.

Only a lowly opinion but the only decent thing installed under your roof iron is a foil sarking purely for sweating and leaks, not really required and as Peter Clark mentioned roof ventilation is a key component for reducing heat transference out of your living space, ceiling or no. Roof spaces get very hot.

The immediate remedy if building or replacing a roof is a reflective colour/material, Zincalum the best, white and so on. Our roof was navy blue currently being replace with a white roof, lots of research led us to a supplier of R3.0 insulation bats, no 3.5 available but the installation of these batts in our living areas 18 months ago led to no A/C and only ceiling fans in those areas. Insulate the ceilings with decent batts, foam what ever and there is a barrier there, ceiling space/living areas. Also batts help to drown out noise.

Effective insulation creates a barrier to reduce heat or cold loss from one area to another, very difficult to accomplish with the rubbish sold here to go under your new roof sold as insulation.

Onto evacuating the roof space of heat requires plenty of eave/soffit ventilation and escape routes for that heat, ridge vents, louvred educts in gables, works in a temperate or cold climate zone for both heat and cold but a tropical climate? Different strokes, typhoons with torrential wind and rain? Not even our windows and doors keeps that out and I have read in past post on expat sites that the educt design ended with sealing the gable ends because they were sick of the leaking ceilings every time a decent storm ravaged their home,,,,,,, best to seal the roof and insulate the living areas at a ceiling level not the source of the heat and happy to hear other opinions.

OMO.

Cheers, Steve.

The "overhang" is almost always 60cm on architect designed homes, primarily to allow most accommodation within the building regs of the subdivision on perimeters. The typhoon rains I've experienced here will throw themselves at the walls and cause ingress under paint cracks or louvered ventilators at gable ends.  If space permits I'd go for 1.5 meters overhang because it does make a difference. I've seen some very poorly made ventilators, plastic efforts that do not stand up to high winds. Always an option is to fit a small window with remote lever down the wall to open and close.