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Metal roofing question

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standupguy
  2/24/2015 11:22 EST

Why don't they put a layer of plywood down first before attaching metal roofing? The home would be so much cooler then & you would save in the long run on air conditioning. Too cheap in the PH.

chance2013
  2/24/2015 15:16 EST

Most houses are built to a price and that would cost money

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poochewer
  2/24/2015 16:23 EST

Have u guys bought any wood lately?
Theres a good reason why houses are mostely made of cement here. For the price of one small peice of wood I can buy 4 bags of cement.
Besides the borers would turn that plywood into dust. Also u would be promoting mould growth as well.

EuroBob
  2/25/2015 01:29 EST

I do not know. Are you thinking that the plywood wood act as an insulator to keep the air from gathering heat as it contacted the metal roof?
Maybe they avoid plywood because they are concerned about termites....or rot, or mold.

standupguy
  2/25/2015 01:39 EST

PC I bought plywood here in Toril. Similar to what I get in Canada, but they call it 'marine PW' here, It's hot down in Mindanao. You would not end up with a solar oven, and it would cost more. More problems if your roof leaks, but mould would not survive the heat. No carpenter ants, powder post Beatles, but possibly termites though we haven't come across any. I would put up plywood if I had to rebuild my roof.

standupguy
  2/25/2015 01:47 EST

EuroBob absolutely it would act as an insulating layer. As for bugs, none have showed in my plywood stash so far. We got mould in Canada where it's wet & cold & dark most of the year. I don't think mould could survive here.

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TeeJay4103
  2/25/2015 05:51 EST

We were advised against using plywood. Reasons were: mold and termites. We used a high gable style roof with ridge and soffit vents for a high attic with plenty of airflow and foil back insulation attached to the sheet metal as it was installed. The house stays cool and the insulation seems to do a good job. Works well for us.

standupguy
  2/25/2015 06:00 EST

@TeeJay4103 - thank you. You are fortunate to have built it right. I agree completely that is the kind of roof I want.

rcampsr
  2/25/2015 06:24 EST

Hello Standupguy,

Due to the type of construction they do here in the Philippines, they would have the added expense of framing the roof with studs in order to hang the plywood on them for proper support, before adding the sheet metal roofing. If you do construct that way, then it would be advisable to place a layer of 90 pound asphalt felt to water proof the installation. Plywood here does not stand up to the heat and humidity, not to mention the insects that will eat it almost as fast as you put it up. Most wood here used for construction is non-dimensional lumber with a nail or two holding it in place. That is why you see most structures and furniture made of cement, steel, glass and plastic to resist the elements here.

I have seen some installations here with a 1 inch reflective backed cellulose foam rolled insulation on them. This is the same type used for insulation on metal buildings in the USA and helps a bit with heat reduction, but contains very little R value. Plywood also has a very little R value. Attic insulation is not used also due to moisture and animal infestations in the attic.

They also do not engineer ventilation into the roofs to relieve the heat buildup during the day and the thermal loading from it in the building. The biggest consideration here is the wind blown rain they have that comes in every crack in the roof occasionally.

Most concrete block homes here are not insulated at all and are just big thermal mass retainers that can heat up all day and then cool off at night. The masonry construction is also sub-standard with bad block, sand, gravel and Portland cement being used. The sand has to be clean in order to provide proper adhesion of the cement to sand. Sand containing no salts or contaminates should be used. Most is beach sand and thus contaminated with salts that affect the cement used to bind the mix together. They also use larger than normal sand and smooth round gravel for mortar and concrete pours thus decreasing the strength.

The steel here is expensive, so they use smaller sizes and/or less of it to save costs in building the structure. The cement mixes are done in small hand batches on the ground and the strength varies from batch to batch. Most block here can be crumbled by hand and lacks strength. The steel placed in the block walls is not tied properly or cored into the wall for strength, so the strength of the wall is also questionable.

Hope this helps, RAC, CBO

standupguy
  2/25/2015 08:48 EST

@rcampsr Good summary & answers to my question. I have seen beach sand mixed with cement. I guess the best thing for me is to go with the one inch reflective backed cellulose and soffit vents. We have thermal loading now that is too much for me. I have experienced horizontal rain & snow in Northern Canada, but here the downpour is like a waterfall. Our house is made of sturdy concrete block as I saw the square hole punched out for my big airconditioner. But other block used for the drainage ditch in front of our gate came apart in my hands. Where are the building codes? Too cheap in the PH.

tlallen59
  2/25/2015 12:11 EST

Our old family house had a metal roof and it would get so hot you could cook an egg on it. After plywood was put on below it, it was cooler for sure but not enough to take an afternoon nap. That's why when I built my house I used concrete and made a walk on roof. It's MUCH cooler but the cost of steel and concrete was a lot.

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rcampsr
  2/25/2015 19:20 EST

@standupguy,

The Philippines has adopted the IBC (International Building Code) as the standard for construction here. BUT, they have added a line to the code adoption stating that if local materials used they are exempt from these standards. Just about 90% of all materials and construction here is made here and there is only 10% that would fall under the IBC standards.

The Philippines falls under Seismic Zone 4 requirements, and the building standards for construction due to its location and seismic activity, and construction here is far from meeting this standard. As an example, San Francisco, CA, USA, is located in Seismic Zone 5 which is the strongest construction required to survive a large major earthquake.

Heat rises in a roof so you may want to add additional ventilation for the hot air to exit or escape the roof. Soffit vents are a good start, but you need to allow the air to recycle out of the attic with some type of peak vent or air turbine. If you use this upper vent, try and add a large drip pan a short distance below the vent so wind blown moisture will be caught and drained out of the attic by a drain to the outside.

Insure all eaves end below the top wall height so if the roof drains get blocked the water will not overflow and run inside onto the ceiling and rain down inside the residence, as happened to me when I first arrived and rented here in the Philippines.

If you do not air condition the whole house, you may also think about a whole house fan in the ceiling to remove heat build up from the interior of the home. Ceilings here are built at an extreme height, 9 to 10 feet above the floor, compared to regular construction at 8 feet high. This will add additional cooling to the attic to help in heat buildup inside the structure. Add wide eaves to the roof system to keep the sun off the exterior walls as much as possible. Plant trees out away from the house to help block the low morning and afternoon sun on the south and west walls of the residence. Locate the rooms that you want to keep as cool as possible on the north and east sides of the home. Do NOT plant trees closer than 15 feet of the house. They look great when they are small, but when they get big the roots will start to lift the structure, as you have seen in many sidewalks in the USA where the trees are planted next to roads.

Hope this helps, RAC

poochewer
  2/25/2015 21:24 EST

You spoke 2 words within the same parragraph, that should not appear together, namely, "regulations" and "philippines".
There are no regulation here, or rather none that either enforcable or are enforced.
I think u people either spend too much time in the US, or in manila.

standupguy
  2/25/2015 23:30 EST

We have steel trusses. Would flat steel sheets be applied to the trusses and then mortar trolled over that? Are there spacific products used? Just curious about how you constructed it.

tlallen59
  2/25/2015 23:41 EST

It is a flat walk on roof that gives us a lot of extra space. We are going to put a laundry room up there and a waiting shed. It was a lot of extra expense for sure but will come in very handy because there is almost no yard. The concrete support beams were done with very thick steel cages and could actually support another floor with a regular roof on it.

EuroBob
  2/26/2015 01:42 EST

In the Philippines, with the houses made of cinder blocks and or concrete, I suggest you pay a lot of attention to how the house is shaded.
Do not let the sun hit the house or a structure which acts as a thermal bridge for heat to enter the house.
So use shade trees and consider a flyroof, a roof to cast shade over your weather tight roof.

rcampsr
  2/26/2015 02:25 EST

Hello Standupguy,

Odds are the trusses were engineered to only meet the load of the sheet metal roof placed on it. If the roof is pitches then you would have to check the engineering specs. on the truss to see what is the dead load that they will support, and what is left for the live load on the roof.

Lets say that your truss will support the load you will have when the roof is complete like you say. You will have to lay the corrugated sheet metal at a right angle to what is normal for good drainage. Then you would have to attach large wire screen to the sheet-metal to hold, support and strengthen the concrete slurry for the roof. Now remember that steel absorbs the radiant energy it receives and then transfers it to the other side where is then re-radiated into the structure. On the other hand concrete becomes thermal mass from the sun, absorbing it and then retransmitting it to the steel and then radiating it into the attic. This will slow the cooling of any thermal mass in the home.

Some people like to place a flat patio roof on their home. To do this you need to check and see if the home was engineered for a cement patio on the roof. The wall footings will be larger, with stronger steel in them to prevent sinking and crack-age. The wall support pillars should have been engineered for the added load. The steel should extend above ti floor level so that it can be used to tie the patio floor into the structure. To help shield the side walls of the structure from the suns heating the patio should overhang the walls by 2 to 3 feet. A wood ceiling should be framed into the structure that can be removed after the concrete has hardened to full strength, approximately 28 days. The overhang should be framed the same way to support the load. The overhang should be reinforced into the house by 2/3 the distance of the overhang with steel rebar. The total area should be reinforced with rebar of at least 3/8 inch to 1/2 inch diameter. Over laps should be 40 times the diameter of the rebar used. They should be tied in 4 to 5 places in equal distance. Lateral supports should also extend the proper distance into the slab for maximum support and properly tied to provide a strong structure. The slab thickness will depend on the load that will be placed on the surface. This is all based on a concrete mix being 6 sack (6 - 90 pound bags of Portland cement) per square yard of materials.

As you can see there is a lot of variation and options to the type of roof used here in the Philippines. The best and cheapest to do is the steel with the reflective insulation under it. Also, use positive ventilation to move the air from the attic to keep the thermal heat to a minimum. They use 1/4 inch plywood for the ceilings here in most homes, but you could buffer that with an attic floor as an added barrier for the heat to pass thru.

Windows are another consideration here. Most are steel frame and glass. there is no sealing of the glass of window frames. A dual pane glass would help with the transfer of heat from the outside of the home. Reflective film would also be an advantage in reflecting some radiant heat.

Unfortunately, swamp coolers do not work well here due to the humidity levels daily. You are going to have to overwhelm the thermal heating of the house by the sun. By doing several things to help reduce heating of the house, the air-con units will not have to work as hard.

Good Luck, RAC

Any14tennis
  2/26/2015 06:54 EST

Hi Standupguy,

One reason for not using plywood I guess is the Termite problem here I have a sheet of ply in my yard and its turning to dust in front of my eyes.....

standupguy
  2/26/2015 08:05 EST

thanks to everyone for all the good information. It has helped me decide on what I can do to cool our house down.

standupguy
  2/26/2015 09:28 EST

Yep, the Canadian termite is not as voracious, but still munches on wet wood no matter how cold it is.

standupguy
  2/26/2015 09:37 EST

RAC - very interesting. Thank you for that!

tlallen59
  2/26/2015 12:29 EST

Poo that is not entirely true. We had inspections and had to make a few changes during construction.

tlallen59
  2/26/2015 12:43 EST

RAC you sure are correct about the steel to concrete ratio with a patio rooftop. And the footings were massive on a 3 story house.

catabisis
  8/17/2015 10:58 EST

Hi rcamper,

I saw your post and wanted ask some questions. Here is your post. It is a little dated. My questions follow your response.

rcampsr
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2/25/2015 06:24
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Hello Standupguy,

Due to the type of construction they do here in the Philippines, they would have the added expense of framing the roof with studs in order to hang the plywood on them for proper support, before adding the sheet metal roofing. If you do construct that way, then it would be advisable to place a layer of 90 pound asphalt felt to water proof the installation. Plywood here does not stand up to the heat and humidity, not to mention the insects that will eat it almost as fast as you put it up. Most wood here used for construction is non-dimensional lumber with a nail or two holding it in place. That is why you see most structures and furniture made of cement, steel, glass and plastic to resist the elements here.

I have seen some installations here with a 1 inch reflective backed cellulose foam rolled insulation on them. This is the same type used for insulation on metal buildings in the USA and helps a bit with heat reduction, but contains very little R value. Plywood also has a very little R value. Attic insulation is not used also due to moisture and animal infestations in the attic.

They also do not engineer ventilation into the roofs to relieve the heat buildup during the day and the thermal loading from it in the building. The biggest consideration here is the wind blown rain they have that comes in every crack in the roof occasionally.

Most concrete block homes here are not insulated at all and are just big thermal mass retainers that can heat up all day and then cool off at night. The masonry construction is also sub-standard with bad block, sand, gravel and Portland cement being used. The sand has to be clean in order to provide proper adhesion of the cement to sand. Sand containing no salts or contaminates should be used. Most is beach sand and thus contaminated with salts that affect the cement used to bind the mix together. They also use larger than normal sand and smooth round gravel for mortar and concrete pours thus decreasing the strength.

The steel here is expensive, so they use smaller sizes and/or less of it to save costs in building the structure. The cement mixes are done in small hand batches on the ground and the strength varies from batch to batch. Most block here can be crumbled by hand and lacks strength. The steel placed in the block walls is not tied properly or cored into the wall for strength, so the strength of the wall is also questionable.

Hope this helps, RAC, CBO

My questions are, are you familiar with terminates in the south? I lived in Virginia. I am not certain the termites are worse here than there.

If one builds a wooden framed house, could they not just treat it with a good termite preventative?

Thanks,
Catabisis

standupguy
  8/18/2015 01:10 EST

catabisis I have seen metal roof venting with the top ridge gap vent space covered from above by a larger ridge cap to prevent the rain from getting in.

They used metal trusses on our roof.

The 90 lb asphalt felt sounds like a good idea.

trotter23
  11/20/2015 19:47 EST

Hi Guys! I just had a very disappointing experience hiring this roofing contractor C-26 Roofing located somewhere along Jake Boulevard Angeles City Pampanga. They provided poor and substandard metal roofs with dents all over. The guys that they sent to work were just kids and inexperience. Very unprofessional. The result is poorly made roofing. I feel I was robe after. Just to warm you guys not to make the same mistake I did.

trotter23
  11/20/2015 19:54 EST

Hi Guys! I just had a very disappointing experience hiring this roofing contractor C-26 Roofing located somewhere along Jake Boulevard Angeles City Pampanga. They provided poor and substandard metal roofs with dents all over. The guys that they sent to work were just kids and inexperience. Very unprofessional. The result is poorly made roofing. I feel I was robe after. Just to warn you guys not to make the same mistake I did.

standupguy
  11/20/2015 21:32 EST

trotter23 We asked our neighbors and turns out one is a damn good carpenter with power tools and skills. Age 33. We had to have our roof re-done 3 times once we bought a ladder and saw the downhill pitch was up against a wall so the rain flowed inside the ceiling. At first recycled roofing was used, Then the wall was built up above the roof line and metal trusses installed. Then the downhill flow went into the gutters and downspouts. If you locate a talented neighbor, they have their community reputation to defend.

BOBV
  11/21/2015 00:41 EST

you heard 6 of one or a 1/2 dozen of the other? Hi the choices are you hire yourself or you hire a company. My experience when i hired myself i had to watch every step. It was no better with a company they pay there laborers 1/3 what i was paying they just perched on the roof all day, besides that the company charged me material and a percentage of labor on top during the project they were taking the materials off my property that i paid for, i was told they going to add additional beam frames on later???these where large beams 6 inches wide guess my roof needed extra support to hold up the birds. i told them i was born at night but not last night, of course they didnt get it.
best advice price it out your self the panels that are pre painted cost about 320 to 380 according to the thickness 4' x 10" over lap by 4" . The metal frame is easy to price at local hardware store, add in paint use epoxy primer and then the finishing coat, rivets, welding rods, gutters and flange with pvc drain pipes and delivery charge. o don't forget the vulcaseal.

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