Ridge vent on mobile home?

I really don’t have a overheating problem with my roof. It rarely gets into the 90s here and it is a dry low humidity type Mediterranean climate.
I only use the central AC about 10 days a year, so I really don’t think I would need that reflective material unless it made a huge difference and lowered the house temperature by 5 to 10 degrees. Plus I really don’t have $2,000 to spend on it.

Where does the reflective material go exactly in the roof design. does it go underneath the shingles themselves and on top of the roof decking or does it go in the attic?
Where would it go in my cathedral ceiling type roof?

It would go on beneath the shingles, in place of the regular underlayment. It could, instead go on the underside of the rafters in the attic, but that is difficult and you also don’t have an attic, so that option doesn’t apply in this case. As I mentioned, some other roofers and contractors will debate its effectiveness, but the arguments are based on a lay understanding of physics and nobody is willing to reconsider their position anyway, so I’m not likely to go into it all again here. The important point is that you don’t have the money for this add-on, and your home is already comfortable and cost-efficient, so you shouldn’t do it.

I just checked the city of San Jose building code and it 150, not 300.
See my separate post on under vented mobile home.

What is the advantage of a ridge vent over square vents?
Does it make the house any cooler, or is it just to make the roof last longer?

In researching venting, I found calculators that determine venting size.
The intake volume is supposed to match the exhaust volume?

UPDATED 8-6-20 9:30am PST
FROM THE ACTUAL BID - THEY ARE ADDING MORE INTAKE VENTS TO COMPENSATE FOR MORE EXHAUST VENTING.
BID WORDING - Install 62 Ft of Ridge venting & 6ea O Hagin vents for In-Takes for proper attic ventilation and Meets Title 24 requirements

PREVIOUS VENT CALCULATION
I found a replacement for the square vent, it says 50 sq inches exhaust.
Galvanized painted black - Overall dimensions: 15 1/2" width x 15 1/2" length x 4" height. 9" width x 9" length outlet with net 50 square inches of ventilation. Made in the USA.

My intake vents under the eaves are probably close to that size, 5x10 approximately.

If you make the exhaust volume bigger than the intake volume,
, like with a ridge vent, won’t that cause problems?

Actually I do have the money for a reflective barrier, if I thought that it would really make a difference of five to 10 degrees in my house.
what happens on many days in the summer is that the house is nice and cool in the morning and then around 2:00 to 3:00 in the afternoon The house starts heating up, and then sometimes we turn on the air conditioning until 7:00 or 8:00 p.m. when the sun goes down.
If we don’t turn on the AC then the house stays hot until the evening.

If this reflective barrier could keep the house or maybe it’s the roof from heating up as much then it would be worth it.

If it was possible we would probably consider putting in more insulation in the roof but I don’t think that would work, cuz there is no space for it to go. So if the reflective barrier, could be a form of insulation, again maybe it would be worth it.

I apologize if I misread your earlier comment. I thought you said that the salesman was trying to sell you on the heat barrier for $2k but you didn’t have the extra $2k. If you do, then maybe you should do a worst-case (best-case?) scenario calculation to determine how long it would take to get back to break-even. Figure out how how much extra you spend on electricity during those hot summer days that require you to run the AC for 5-6 hours. Figure out how many days per year you do that, and then divide to see how long it would take to save the $2k if you never had to use the AC ever again.

Well worst case would be that it makes absolutely no difference.

Best case would be that it makes 10° of difference which would be huge, and I probably wouldn’t need to run the air conditioner hardly ever.

But I would need some pretty strong evidence that it would work in my case with a similar roof and house as mine.

But at this point in time there is no way to know about the best case scenario, once I can find someone with a similar roof I’m similar mobile home as mine.

So what I’m going to do is use the contractor with the ridge vent, which triple the venting capacity and bringing it up to San Jose city standards which is based on the 150 formula.

What I meant was I didn’t have that 2k for a very uncertain cooling gain.
And after doing some more research on the reflective barriers.
What I had read is basically that there has to be some type of air gap between the reflective surface and the shingles.
So the best place to put it would be on the underside of the attic rafters if it was possible to get in there which it isn’t.
I think this was basically what you said in an earlier post.

And your ridge vent investment without an air gap between the insulation and the roof deck. SJ city standards don’t mean anything without that…

You can absolutely follow through on your best case analysis. Finding another homeowner with a similar home and the same product installation will tell you nothing about your best case, only about a possible similar outcome. Unless the other house is in the same area of the world, same tree cover, same type of use of the house (# of times the doors open during the day, etc.), same kind and efficiency level of HVAC equipment, etc. it will be impossible to do an apples-to-apples comparison.

You have to do a little work but the arithmetic is trivial. Or use a site such as EnergyUseCalculator - dot - com ( http://energyusecalculator.com/electricity_centralac.htm ) . Check the labels on your AC equipment and your electricity bill to get the numbers you need.

For instance, if you normally use your AC for 6 hours per day for a solid 3 months every year and your AC uses 3500W of power and an electricity rate of $0.10/kwh, then your best-case (no AC use at all) would save you 10.5 years to hit the break-even point.

The research you did is based on a flawed understanding of the thermodynamics of roof structure, because the most prominent info on the web is from sellers/installers of radiant barrier films or paints (competing products). I was a physicist long before I got into roofing. Like I said a few msgs ago, I’m not going to dive into this debate, but info that discounts heat barriers out of hand is just simply hogwash. The only thing that matters in the end, however, is not the science or theory but whether it makes the home more usable, comfortable, or cost efficient.

I previously explained that the choice of shingles is important in this situation as some are more sensitive to under-ventilation than others. Ventilation is BY FAR the most important choice you will have to make and there is no way whatsoever to know what type you need to use (or even can use) until you take off the shingles and several sheets of decking to inspect the structure.

So, run your AC cost analysis, strip the roof, pull some decking, document what you find, replace the decking, dry it all in with “felt”" (use synthetic underlayment, not asphalt-impregnated paper) and then you can sit down at your kitchen table and figure out exactly what options make sense and which ones don’t. Then you can pick your shingles, decide on the ventilation, decide on the heat barrier, order it up and do the project. If the house is dried in properly (pay special attention to any valleys), then it will be fine for it to sit for a few days while you sort out the options. The only downside that I can see is that you might end up paying for underlayment plus heat barrier, instead saving the cost of the underlayment, but you’re only talking about one man-hour of labor and $100 in materials, so it isn’t that big a risk.

-neville

jgcec
August 7

Well worst case would be that it makes absolutely no difference.

Best case would be that it makes 10° of difference which would be huge, and I probably wouldn’t need to run the air conditioner hardly ever.

But at this point in time there is no way to know about the best case scenario, once I can find someone with a similar roof I’m similar mobile home as mine.

So what I’m going to do is use the contractor with the ridge vent, which triple the venting capacity and bringing it up to San Jose city standards which is based on the 150 formula.

What I meant was I didn’t have that 2k for a very uncertain cooling gain.
And after doing some more research on the reflective barriers.
What I had read is basically that there has to be some type of air gap between the reflective surface and the shingles.
So the best place to put it would be on the underside of the attic rafters if it was possible to get in there which it isn’t.
I would be convinced if I could find a referral of a similar type mobile home owner as myself that has used it and has noticed a noticeable cooling effect with it.

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I re-read your last post on inspecting the roof as the first step.
Thank you,

Do you still have any of those pictures of a ridge vent on a mobile home?
The previous links don’t work anymore.

How much would it cost to pull up enough roofing to determine if a ridge vent would work?

CONTRACTORS RECOMMENDING RIDGE VENTS
Only 1 in 7 bids,
oops actually 3 in 7
recommended a ridge vent
and that was only because of the GAF or OC extended labor warranties.

2 of the 3 high end roofers with the highest bids recommended the ridge vents, that discovery makes me feel better.

Would a ridge vent make that much of a difference temperature wise?
Or is it only to make the roof last longer?

I am thinking that the only thing that will definitely make a difference temperature wise is an almost white shingle vs a much darker one.

Another video against mobile home ridge venting.


An asphalt shingle is a heat sink and it is out in the sun all day.

No matter what kind of uv resistant coating a shingle has it is going to heat up and retain heat this heat is going to conduct through the sheeting into the attic space.

The way to deal with this heat is to vent it out of the attic space.

Keep in mind that all this literature that you are reading regarding uv resistant shingles and various ventilation schemes is written by entities that are trying to sell you on their product.

Did any of these roofers you have talked to appear intelligent?

Maybe you should listen to the ones that at least appear intelligent & knowledgeable.

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The only one that fits that description is Norman Ball a senior product manager at Cavco, the company that bought Fleetwood.
He has 50 years experience in the mobile home industry.

https://www.linkedin.com/in/norman-ball-14226643/

Can you tell me what are the two kinds of cathedral ceilings structures that will allow a ridge vent and which ones will not?

My first question for them would be have they done any ridge vents on mobile homes?

Does this picture of the inside of my house tell you anything
about the roof structure?

Thank you,
It never rains this time of year in California. First rain is end of September.

I went to buildzoom to get some more bids.
I guess I will also go back to the 3 roofers that recommended ridge venting and see if they are interested.
I will go and search on Yelp to find any reviews about mobilehomes.