New roof advice

[simoh1490]

11 minutes ago, Sheryl said:

But what makes the gable vents exhaust? Wouldn't they also draw in air from their lower slats? I'm confused because I can't see how the gable vent and the vented soffits will behave any differently except to the extent that the soffits are lower down.

 

When you say all the overhang is this including sides of the gables? And what about the soffit under the eaves at the bottom of the gables which don't seem to connect to the attic? (Though I say that from looking at a distance, haven't crawled on my belly all the way to them to peer downward)

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"I'm confused because I can't see how the gable vent and the vented soffits will behave any differently except to the extent that the soffits are lower down".

 

Sorry again, I didn't explain this fully. Hot air leaves by the highest point (gable vent), cooler air is drawn in from anywhere below that point.  If that point is two inches below the gable vent that cooler air is only going to be marginally cooler than the air above it. But if that cooler air can be made to be drawn in from a lower point, it will almost certainly be much cooler hence the airflow will be greater and faster. Clear?

[Sheryl]

Yes, OK - so the soffit vents do indeed have to be well below the gable vent.

 

Any thoughts re putting the soffits below the eaves at the bottom of the gables? As mentioned doesn't look to me like it connects into the attic space, those tiles for instance don't attach to the other roof tiles at any point - but maybe someone knowledgable about usual gable construction in Thailand would know.

 

Otherwise all I can do is both sides and a small section in the middle at the back.

The sides measure 12m each so could take 10 soffit boards each, I can get maybe 2 more in at back so 22 in all, by your calculations about 165 sq m of ventilation.

 

I'm not sure how to estimate attic area given that the sides slope inward. It is 10 x 14 meters at the base and the upward slope is 3.7 meters.

 

Tutsi: don't worry, misery loves company, you are welcome to join in this thread (you may not be miserable yet but you will be when you start working on your roof...)

 

Personally I considered and rejected both ridge vents and those mushroom-shaped rooftop exhaust fan things, in both instances out for fear of risking leaks. (All anyone has to say to me to deter me from something, roof-wise, is  that it might leak. While the torrental-influx-of-water-from-roof episode is some 15 years ago the trauma lingers...). Where I live really, really torrential rains (literal sheets of water kind of thing) with winds are the norm.  And it often comes in virtually horizontal, on winds from the south. I can readily visualize it it getting up under a roof ridge....I think you are in Issan so you will have much less of it - I am on the southside of the Issan plateau and all the rain you do not get, is because it doesn't make it over the mountains and rather dumps onto my house

But still you will have a few pretty big storms each year.

 

 

[simoh1490]

Unless I'm misreading what I see when looking at your photographs, there is quite a long area to the front of the house where vented soffit boards can be installed. It is probably pointless to install them under the eves of the actual gable units themselves (the higher points in the front that house the two gable vents) but the overhang underneath those points is an absolute must. Ditto the back of the house, there's an area of overhang to the left and the right of centre where that room with the (louvered?) windows sits that can accept vented soffits. In summary, the only area potentially where you appear not to be able to install vented soffits is the middle of the back of the house.

 

Ridge vents and whirlybirds are entirely dooable as an alternative, you've had one very bad experience of flooding from the roof which should not be allowed to cloud your views on this. BTW I keep loosing the TVF internet at the host hence the long periods of no reply.

[simoh1490]

I just noticed my calculation for vented soffit board in post 385 earlier is wrong, it is, of course, 0.5cms x 15 cms X 24 holes per board = 180 sq cms per board. To convert to square feet multiply the answer by 0.00107639104, so one board contains 0.1937 square feet of (input) ventilation space.

[Sheryl]

1 hour ago, simoh1490 said:

Unless I'm misreading what I see when looking at your photographs, there is quite a long area to the front of the house where vented soffit boards can be installed. It is probably pointless to install them under the eves of the actual gable units themselves (the higher points in the front that house the two gable vents) but the overhang underneath those points is an absolute must. Ditto the back of the house, there's an area of overhang to the left and the right of centre where that room with the (louvered?) windows sits that can accept vented soffits. In summary, the only area potentially where you appear not to be able to install vented soffits is the middle of the back of the house.

 

 This overhang is what I have been asking about..because it does noy seem to connect to the attic. From inside the attic, the floor meets where the gable vent is. And the tiles on those overhangs do nto connect to the rest of the roof. So how can it send cold air into the attic?

 

Middle of the back of the house can be done, only problem is the large light fixture but can work around that.

[simoh1490]

OK, the pictures in post 25 seem to confirm the story on that, it's visually unclear from the most recent pictures what that arrangement is. The attic floor is higher than I had imagined, the overhang under the gables (as opposed to the overhang next to the gable vents) doesn't permit a cool air feed into the roof void. The bottom line is, there is no point in putting vented soffit boards into areas of the roof where an airflow to the peak of the roof cannot be created.

 

But those two areas of roof might become a problem later from a thermal perspective - you're going to re-roof those two areas of roof AND install RB under it, the question is, what will sit underneath the RB? My guess is that under that area of roof is an air gap and then the ceiling of the living area, if that is the case you may wish to consider filling it with layers of foil encased fibre glass insulation to deaden sound and also protect against heat transfer into the room. You will know better once you've stripped off the roof and can see inside.

[simoh1490]

In respect of the total surface area of vented soffit boards:

 

You can only install them where it is practical to do so, it's not as though you can create additional overhangs that vent into the roof space. You wrote that you think you might be able to get 22 vented boards installed, that's 22 x 180 sq cms. or nearly 4 sq meters which is very respectable. What you might do is ask one of your workmen to measure the gable vent, measure the width and height and then the size of one of the air gaps, also count the number of air gaps per vent. That way we can calculate what the volume is of air in versus air out and determine the shortfall of air out.

 

We can address that shortfall a number of ways, as described earlier: you aren't keen on whirlybirds but you might reconsider this as an option. A better option for me is to make the existing gable vents larger, a third option is to instal an exhaust fan at one or both of the gable vents and this will force air out and actively draw in cooler air through the soffits. I have a fan that sits behind one of my gable vents, it cost about 1,200 baht and installation is simple.  If you go down this route the fan should be connected to a thermostatic switch so that it will switch on and switch off again at predetermined temperature settings, a domestic heating and cooling switch can do this job and they cost about 500 baht each. Lastly, a 0.75 hp fan consumes three-quarters of a unit of electricity per hour so figure about 3.3 baht per hour to run - mine runs about three hours per day but only during the very hot weather, about an extra 300 baht on the electric bill for a few months per year.  

[carlyai]

That is unquestionably the wrong thing to do and you are right to be concerned at closing up the eaves, anything less than 90% air intake coverage is a seriously bad idea, especially since you're now trying to tackle a heat problem. By all means close the eaves to prevent rodents but for goodness sake don't limit the soffit intake at 40%. If you look back at a previous post I made on the subject of airflow, you will see that: the amount of airflow in space MUST equal the amount of airflow out space. And, the flow of air through the attic/roof void must be relative to the size of the roof and its footprint.
 
Put another way - a cumulative two square feet of intake air (from vented soffit boards), combined with a gable exhaust vent of five square feet, results in airflow of the lesser amount, two square feet! Make your vented soffit board area as big as you can now (90% would be great). If you find out later that your house is still hot and you don't have good airflow, increase the exhaust (gable) vent size and things will improve.
 
Carlyai - sorry, but your friend was very  wrong on this point.

That's great to know because I've got slatted soffit on all. Just covered up with foil:sigh


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[simoh1490]

I've been studying al the photographs again and there may be an issue.

 

I may be wrong but it looks as though there are only two parts of the roof that have hot air exhaust vents and they are the two peaks to the left and right of the house when facing it. The remaining parts of the roof do not have hot air exhaust vents so my questions are:

 

1) is there internal access to the centre part of the roof at the back of the house from the two peaks that contain gable vents - put another way, can hot air contained in the roof at the back that runs left to right in the photo's, find it's way into the two peaks that run front to back in the pictures and that contain the gable vents? If the answer is yes, airflow through those three parts of the roof shouldn't be a problem.

 

2) Does the new smaller roof in the centre, the one that has large valley gutters on either side, have access to the larger roof section at the back of the house that runs left to right? More concisely, once inside one part of the roof, is it possible to access all other parts of the roof or are some parts closed off and separate? If the answer to this one is also yes, there's no issue.

[wayned]

The soffit vents that I am used to are like these and omly require rework for the existing boards, cutting a rectangular hole, to install:

 

[simoh1490]

2 minutes ago, wayned said:

The soffit vents that I am used to are like these and omly require rework for the existing boards, cutting a rectangular hole, to install:

 

Yes, I've used something similar but smaller. There's no doubt using grills to cover large holes cut in the overhand can work but they are not especially cost-effective versus vented soffit boards. Also, the amount of air gap in the grills by comparison to the vented soffit boards is much smaller. I started out by using cooker hood vent grills which were effective but horribly expensive at 250 baht each, vented soffit boards are only 35 baht or so and provide six times the airflow.

[wayned]

13 minutes ago, simoh1490 said:

There's no doubt using grills to cover large holes cut in the overhand can work but they are not especially cost-effective versus vented soffit boards.

I have never seen them here, nor have I looked for them.  In the US they can be found in every building supply store along with facia board vents and are the most common way of venting..   They are made out of anodized aluminum and are not expensive  I don't have soffit vents in my house, only the plastic vented eave vents that fit the contour of the roof tiles, but if I wanted to add soffit vents at minimal expenditure I would use these as I think that  could retrofit them to the front and back of my house by myself in one day if I had my H&A wired together! They also come in 4' and 10' sections so that you can install them on the entire length of the soffit.

[simoh1490]

As I recall wayne I went looking for similar here couldn't find them, it wouldn't be the first time I tried to find a simple building product like that in Thailand and failed!

[Sheryl]

8 hours ago, simoh1490 said:

OK, the pictures in post 25 seem to confirm the story on that, it's visually unclear from the most recent pictures what that arrangement is. The attic floor is higher than I had imagined, the overhang under the gables (as opposed to the overhang next to the gable vents) doesn't permit a cool air feed into the roof void. The bottom line is, there is no point in putting vented soffit boards into areas of the roof where an airflow to the peak of the roof cannot be created.

 

But those two areas of roof might become a problem later from a thermal perspective - you're going to re-roof those two areas of roof AND install RB under it, the question is, what will sit underneath the RB? My guess is that under that area of roof is an air gap and then the ceiling of the living area, if that is the case you may wish to consider filling it with layers of foil encased fibre glass insulation to deaden sound and also protect against heat transfer into the room. You will know better once you've stripped off the roof and can see inside.

Yes, there is an air gap and then the ceiling of the two bedrooms at either side and in the middle at the front (under the small gable roof) there is a landing where the stair from the first floor comes up with a sitting area that faces a fully glass/screened-in wall (sort of a semi-porch, replacing the original design of an upon porch). In the  back under the middle back, non-gabled  roof there is a sort of common area.

 

In answer to your other question - excluding that little front area under the smaller gable, the attic is all open and can easily move from one part to another so air entering at the sides has no obstruction to moving throughout the attic and exiting the gable vents. There are  4 gable vents, one at each end of the 2 side gables.

 

Under the front middle gable (added on after the house was built) the attic space has only small connection to the rest of the attic-  maybe 3 inches high and at the bottom. My cat can easily pass through as can all other critters but a person cannot. So some air movement but not unimpeded. This spot is the hottest in the house. It currently has no gable but I will add one. Due to small space and a T-shaped wooden support behind it will have to be custom made. Maybe 4 small round vents.

 

I just conferred with the workers explaining the need for air intake to be lower than the exhaust vents and we walked all around figuring out where it can go.  It will be under eaves all along the 2 sides of the house and also the small area in the middle of the back. For the area at front, there is no where to put at the gables on either side, but as the attic space is wide open hopefully the venting along the sides will make up for this.

 

Under the small middle gable it was suggested to install the vented boards inside the house in its middle ceiling, which is not hanging but rather just 2 large boards nailed onto a wooden frame (see pix below) so perfectly possible to do. The windows in that area are kept open most of the time  and in the day time I also have a wall  fan running so there is air that could be drawn up, what do you think? Otherwise I think we will have adequate (or at least much improved) ventilation under the original 3 roofs but that middle area will not have enough.

 

 

 

[simoh1490]

It sounds like you're in pretty good shape, I would strongly recommend insulating the void/air gap mentioned above.

[Sheryl]

23 minutes ago, simoh1490 said:

It sounds like you're in pretty good shape, I would strongly recommend insulating the void/air gap mentioned above.

But won't that will defeat the purpose of the soffit boards in the ceiling there. ? I can't have insultation laid atop vented soffit.

[simoh1490]

28 minutes ago, Sheryl said:

But won't that will defeat the purpose of the soffit boards in the ceiling there. ? I can't have insultation laid atop vented soffit.

I am refering to post 404 which reads:

 

"But those two areas of roof might become a problem later from a thermal perspective - you're going to re-roof those two areas of roof AND install RB under it, the question is, what will sit underneath the RB? My guess is that under that area of roof is an air gap and then the ceiling of the living area, if that is the case you may wish to consider filling it with layers of foil encased fibre glass insulation to deaden sound and also protect against heat transfer into the room. You will know better once you've stripped off the roof and can see inside".

 

Unless I misunderstand you seem to confirm those parts of the roof DO NOT feed into the roof cavity hence they don't require soffit boards, in which case they should be insulated.

 

[Sheryl]

Sorry if not clear, I'll try again:

 

The gables at either side of the house DO connect directly to the roof cavity, unimpeded. Beneath them are the two bedrooms, and between them, is the cavity created by the back middle roof, beneath which is a sort of living area. This whole roof cavity, a sort of U shape , is open. This is the original house design with the open area in front having no roof.

 

What does not connect are the overhangs below the gables. These have nothing under them, they just jut out from the house. So I will not be putting RB beneath them and there is nothing to insulate there.

 

The middle front area (with the small gable) has its own attic space which connects to the rest of the attic only by a rather small space. This is what I thought you were saying to insulate and was where I was going to put vented soffit into the ceiling. HOWEVER, I finally stuck my head up into that space and it turns out that this ceiling is lower than the others and does connect to the overhang, so the front middle overhand can have vented soffits. See pix

Any idea as to how I can construct evae vents around that wooden "T" beam most welcome.

[Allen Ginsing]

You could put a ridge vent on top.  Not sure that you need it, looks it is separate from the top of the house.

 

https://buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting/view

[simoh1490]

4 minutes ago, Sheryl said:

Sorry if not clear, I'll try again:

 

The gables at either side of the house DO connect directly to the roof cavity, unimpeded. Beneath them are the two bedrooms, and between them, is the cavity created by the back middle roof, beneath which is a sort of living area. This whole roof cavity, a sort of U shape , is open. This is the original house design with the open area in front having no roof.

 

What does not connect are the overhangs below the gables. These have nothing under them, they just jut out from the house. So I will not be putting RB beneath them and there is nothing to insulate there.

 

The middle front area (with the small gable) has its own attic space which connects to the rest of the attic only by a rather small space. This is what I thought you were saying to insulate and was where I was going to put vented soffit into the ceiling. HOWEVER, I finally stuck my head up into that space and it turns out that this ceiling is lower than the others and does connect to the overhang, so the front middle overhand can have vented soffits. See pix

Any idea as to how I can construct evae vents around that wooden "T" beam most welcome.

OK, gotcha on the first part.

 

On the second part: am presuming you meant to write , "how I can construct gables vents" rather than eaves vents? There's a number of options:

 

1) a custom grill such as wayne posted earlier, fitted just under the cross - it would allow some hot air venting out.

2) insulate the floor of that space, install vented soffits and don't instal any gables vents. What will happen there is the insulation will protect the ceiling of the living space and as the hot air in that space expands, it will be forced out of the vented soffit boards. This is the reverse of what a vented soffit board is before but it's actually the way roof venting is done for most newer houses in Thailand, odd as it may seem (and it is odd). If you do that, the key to sucess will be making sure you have enough foil encased batt insulation on the floor .

 

 

[Sheryl]

Thankd -- and yes meant to say gable vent.

I will insulate the space, easy to do as no hanging ceiling wires in the way.

I don't understand putting gable vent undrr the cross as that is already the eaves space. Was thinking of makine round vent holes in eavh quadrant of the T right on the gable. Just wondering if thete is anything commercially available to use for the frame.

I am a little worried to use only vented soffits + insulation and no exhaust vent. There is a post in the "cool thai house " that tells of pressure building up in the roof during a storm and blowing the soffits out. I'm not sure how that unless he lacked exhaust vents? could happen

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[simoh1490]

3 minutes ago, Sheryl said:

Thankd -- and yes meant to say gable vent.

I will insulate the space, easy to do as no hanging ceiling wires in the way.

I don't understand putting gable vent undrr the cross as that is already the eaves space. Was thinking of makine round vent holes in eavh quadrant of the T right on the gable. Just wondering if thete is anything commercially available to use for the frame.

I am a little worried to use only vented soffits + insulation and no exhaust vent. There is a post in the "cool thai house " that tells of pressure building up in the roof during a storm and blowing the soffits out. I'm not sure how that unless he lacked exhaust vents? could happen

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I think we may both be saying the same thing except using different words. Looking at that cross.....that is the outside wall and you need/want to put a hole in it to let hot air out. That being the case, however you do it will work. My solution was to cut a hole(s) in the wall, just under or above the latteral arm of the cross and cover with a metal or plastic grill.

 

Pressure building up/blow out. It's got to be a rare set of circumstances to make that happen but it does support what I've said a few times that the size of air in must be the same as the size of air out.

 

If you look at new houses in Thailand, most if not all have a four-sided hip roof that rises to a point in the centre. They will have installed RB and there will be a vented soffit in the four corners of the eves but that is to allow hot air to escape (hot air expands). So no gables vents or hot air out, only minimal vented soffits used in a reverse manner plus no fibreglass insulation on the floor of the roof void, crazy.

 

Whilst I think you will probably be OK if you don't install a gable vent, a belt and braces approach might be to cut a hole in that wall and cover it with grill of some sort - you could even install vented soffit board, cut to fit and installed vertically in the areas above and below that cross, that could work although there's small risk of blown rain getting into the attic through the vent holes.

[Sheryl]

Thanks. Any idea what I can buy to use for grill?

The poster with the blown out boards nrntioned having put in only 4 and at the corners so likely the common practice you describe.

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[simoh1490]

5 minutes ago, Sheryl said:

Thanks. Any idea what I can buy to use for grill?

The poster with the blown out boards nrntioned having put in only 4 and at the corners so likely the common practice you describe.

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You'll just have to wander around a large hardware store/builders supply merchant and see what you can spot. Before I installed vented soffit boards and did the job properly, I installed cooker external vents which are widely available and for a small job like that one they may well work OK. They're plastic lovered vents that come in two sizes and look like this:  http://www.i-sells.co.uk/louvred-grille-125mm-spigot-white

[carlyai]

You may find it in a big electrical store that could have spare grills for exhaust fans.

I did see a similar looking one in the swimming pool section at Global House Roiet yesterday. Not sure if all Global Houses would carry them.

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[Sheryl]

Just found this in Home Pro!

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[simoh1490]

8 minutes ago, Sheryl said:

Just found this in Home Pro!

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They come in two sizes, I have ten (10) of the smaller ones installed in places I couldn't fit vented soffit boards. They work, they're not cheap, given the amount of air intake, but for the application we just discussed, probably a good, quick and easy solution. P.S. paint them as necessary to hide the grill work.

[Sheryl]

Got the smaller side, 4 of them will put 1 in each quadrant of the cross shaped beam

 

They are costly for what they are, agree. And they won't last as long as the thick wooden gable vents (mine 20 years on, are in great shape still). 10 years max, maybe less. But  serves the purpose and beats trying to construct my own.

 

The roof tiles & accessories (including eaves filler) will be delivered Wednesday, supplier was able to expedite things with the factory. Came to 39K inclusive of delivery.

[simoh1490]

That all sounds good. Perhaps you'll consider posting some pictures of the work in progress, once it gets underway, maybe we can spot things for you to think about as it goes forward? To be honest, your work crew sounds like they know what they're doing and that's no surprise, lots of folks knock the average Thai/Cambodian worker for not knowing much at all but my experience is they know plenty so I doubt you'll get led astray.

[wayned]

7 hours ago, simoh1490 said:

o be honest, your work crew sounds like they know what they're doing and that's no surprise, lots of folks knock the average Thai/Cambodian worker for not knowing much at all but my experience is they know plenty so I doubt you'll get led astray.

I agree and what they can't buy they will somehow fabricate.  When those old roof tiles come off they could soon become siding and roofing for a Thai house which will be much better than they currently have.  Filling the holes from the bolts is no problem,.  They wouldn't go buy caulking, but make their own by mixing benzene and insulating foam, instant "Naplam"!, but it works fine, but definitely flammable!