For the roofing experts - I bought a mobile home on the main ranch where I hunt and work sometimes in South Texas.

Currently it has asphalt shingles. They are patchy in spots where wind blew some off, but there are no big bare spots. High winds, 50 - 60+ mph are common every year.

It is on the west side of South Texas, about 100 miles from the coast. Temperatures are 105 - 110+ in August and September.

With those factors, can gavalume sheets be screwed into the existing shingle layer or do the shingles need to be removed and/or put down furring strips?

This is a camp house, not my residence. So trying to keep a lid on repair costs, but not have the roof leak or blow off.

Thanks guys.

I'd remove the shingles......if you're going to the trouble to do it you might as well do it right.

Weight would also be a concern. I would remove the shingles.

This.

Put 1x4's up every 2 feet horizontal and fasten to them over the shingles
...That gap lets heat escape...

It’ll be fine over a layer of shingles.

Some places wont insure a roof unless the old asphalt shingles are removed.

If it was a good idea they'd build houses like that to start with.

Removing the shingles isn't that hard.....the clean up's the worst part.

Do it right and forget about it.

All good metal roofs will have a waterproofing layer under them....either asphalt based or some woven textile with an adhesive.

If it will support the weight, and the shingles are still waterproof (apart from the area where they are missing), leave them. As above, stand the metal panels off from the shingles for ventilation.

Yep. Did it this way as a matter of course back when I worked for a roofing company except we generally used firring strips rather than 1x4's. All of this assuming there is only one layer of shingles on the roof. If more then they should be taken off.

^^^^^
I know of contractors that will not warranty the work or the material's if they are installed over any other roofing material.

Why?

^^^This^^^

As said already, At the very least screw or nail (screw more better) some purlins every 2 feet and attach the metal to the wood purlins. Removing the old shingles is the best.

I placed a white steel roof over asphalt shingle with 1" firring strips between on our 1400 sq ft home. I would not change that as the A/C unit works far less now with that extra bit of insulation. I can see no downside to this type of roofing job. It is very commonly seen around here.

so they can get out the warranty......and make the money in the tear off...…..bob

Your work is subject to the quality of previous work and materials.

Stripping to decking allows you to examine and address any structural deficiencies.

Exactly why.

Because they can rape the home owner for the additional cost of stripping the old shingles.

Note, do not lay steel directly upon the aggregate surface of asphalt shingles, as the aggregate will scrape through the paint and zinc which will allow the steel to rust.

Rape the home owner??



If the asphalt shingles are so good why are they being covered up with tin??

Money burning a hole?

Personally, I would tear off. But, a lot of folks around here seem to go with metal on top of 1x2 or 1x3 furring strips without any issue. If I were going to do that, I would at least use 2" to 3" deck screws to anchor the furring strips...

Metal for this location because asphalt shingles blow off in the heat and high winds.

There are 100 year old roofs in the area covered with corrugated galvanized sheets.

Rainfall is 12” - 18” most years, and most of that occurs in six weeks in the fall and six weeks in the late spring. Some years rainfall is in the single digits. However, a tropical storm can come in and drop 20” in a day or two.

But it mostly is a true desert area.

As said earlier , 1x4 strips every 30” . The last three I’ve done on my places I put reflective insulation under the steel and it really knocksthe heat off. It’s basically bubble wrap with mylar to reflect. No need to strip the roof and don’t put the steel directly on the shingles. I just did a 16x80 single wide and did it in an afternoon with three 50ish year olds. Not really that hard.

Sounds right.


You counldn't beat me hard enough to have an asphalt roof.


No way I would nail through that schit to mount a tin roof.

.


This

You see a lot of them around here put on over old shingle roofs with the furring strips, they hold up fine it seems. If it's a trailer camp that's what I'd do, I wouldn't go to the trouble of pulling off the old shingles. Use long screws so they'll go all the way through and get a bite into the decking.

The asphalt was good 20 years ago. But it had started to curl and shingles blow off.

I put three inch screws through firring strips, the shingles, sheeting, and into the rafters. The firring strips are not coming off. And the steel will still be there long after I am dead.

Right on the shingles if you live in a snowy area.Putting them on furring strips is asking for ice dams.

Ideally, I would remove the shingles, apply 60lb asphalt roll membrane, then screw the galvalume over that. The asphalt underneath helps to keep the screws from loosening and provides a seal if they do loosen. Also, asphalt can provide a protective barriere against insect infestation. GD

I nailed 1x4s to the truss on top of the shingles 24inc between 1x4s .cut 4x8 3/4 sheets of foam in haft . been all most 30 years with on prob. you don't have to worry about were you step with the foam between the 1x4s

I wouldn't do it.

Not into it, THROUGH it, and all the way through the decking, too.
With only 1 layer of shingles, especially if they're 3 tabs, weight won't be an issue. The metal isn't enough added weight to matter.

EXactly!

As usual lotta folks here want to make stuff more complicated than it is. We did many dozens of metal roofs using firring strips over shingles without problems and that was in upstate NY where we get plenty of snow, rain and wind..

This.

This is what we did over 20 years ago. The electricity usage for A/C went down by half. We used the silver shiny Galvalume that reflects heat very well. The 1X4s should not be treated wood because the treat starts corrosion and the warranty would be void is what I was told. We have about 50 inches of rain a year and so far so good.

I had weather damage 7 years ago and my insurance company paid for a new roof. I had already replaced one roof 20 years earlier and did most of the work myself. The cost to put metal over shingles with no tear off worked out close enough to the same price as tearing off the old shingles and replacing with new. Seemed like a no-brainer to me. My roofer used furring strips and cut the vent pipes flush with the roof. Everything vents just as well as before and there are no holes in the roof for them. I've been very happy with the results and have noted lower heating and cooling costs as well. This roof will last the rest of my life. Had I gone with shingles I'd be doing it again in another 15-20 years. I hope I live another 20-25 years.

Yup!

If it's one layer of shingles, leave them.
If it's been shingled multiple times, remove them.

Get those shingles off, get a good view of your decking, make sure nothing is rotten.


If all good, cover with #30 with rag felt, mark the rafters and commence to nailing on 1x4 or 2x4 lattice.

Allows for a solid piece of meat to fasten your new metal roofing to.



I've done a couple dozen like this^^


That screwing metal to shingles is a half ass deal. Only if youre lucky will any screws hit a random rafter. Otherwise your punching into brittle 3/8" to 1/2" plywood.
About like zipping screws into a pumpkin rind.

And the bees love it too.

If you still want to go the halfass route, 1x4 over the shingles. Make sire those 1x4s are attaching into rafters. Preferrably wth a 8p ring shank.

The weight myth is a non issue.

Cap those 1x4 exposed edge off with 'mini corner'

Fugg the air gap

Cut 1-1/2" wide strip out of that old decking at the ridge cap. It'll vent with perforated vented ridge capping

Because it means warranting materials you did not install, and labor you did not provide. That previous roofing material is already compromised, or it wouldn't need repairs. It may sag, swell, shift, buckle, or separate, dragging the new material with it, causing issues that the roofer will have to fix. It's a simple case of avoiding a possible problem later.
As for the weight issue being a myth, that is not true. It varies from place to place, but either 3 or 4 levels of shingles is the max for a "nail over".
I grew up in the construction trade, worked as a roofer, carpenter, punchout man, drywall, masonry, I ran one of two crews for a general contractor.
Something not mentioned is the pitch of the roof. That has a great deal to due with the acceptable load on that roof. You will note that areas with high snow fall, also have sharply peaked roofs, so the snow load does not collapse the roof. (Helps to have an Engineer for a father)
I, personally, will not do a "nail over", even if they are legal for a couple of layers. It's half-assed, it does increase the roof load, and it does not expose problems with damaged or rotting roof members or sheathing. (You can't see it, so you just don't know. )
I would suggest doing the tear off, and examine the wood beneath, correct any issues you find, then reroof.

Lattice is not required if you have decking already. Just staple down 15 pound felt and then screw the metal directly . Lathing , lettuce or whatever you call it in your NoW is not required or needed.

I agree with Slumlord, and Kellory. Listen to these guys. Unless you tear off the shingles you have no idea what is below, or what the condition is. Once you get it done and inspected you are ready to go. Unless you already have shingles off, you really have no idea what the condition of the decking is. If the decking is OSB then use 1X3 or 1X4 strips to screw to. The manufactures of metal roofing I've seen throw your warranty out if it's not attached to plywood. IF it's 3/8 ply you have the same problem. If it's a concern to you, why haven't you talked to the company providing the metal? If you want their warranty, find out what THEY require.

It’s always best to tear the old asphalt off but, if you opt to leave it on, you’ll want to construct a cold roof.

the guy is talking about an old mobile home he camps out of......looking to keep it as low cost as possible, in this case furring strips over the shingles will work.

would I do that on my house ...no...…..kellory ..I am a general contractor....anytime someone lists 4,5,6 jobs in the trades that he does., usually means he isn't good at any of them.....bob

What year is the mobile home? Single wide?

It’s not hard to tell if you have weak spots in the roof. Is it leaking now?

Since you’re trying to save money and all, go ahead and rip out all the paneling on the inside. Better make sure there’s no termites or black mold.

Remove the shingles. Put down ice and water shield and screw a metal roof on it.

Double wide, 7 - 8 years old, 50 x 27, nice condition overall. Leaking in one spot over the door five or six feet from the dripline. Shingles where blown off in a few places and will leak when the rainy season starts in September or a tropical storm blows in, whichever comes first.

fyi - the nearest roofing supply house is 80 miles away one way in San Antonio. So it’s not like working a job in a city.

Thankfully I found a good HVAC man nearby- only 40 miles away. He does not know a single roofer anywhere close as they are working in the oil patch jobs now.

Find the closest manufacturer of steel roofs. Take him the measurements of your roof and he will custom build your entire roof including all endcaps, centercaps, screws, etc, and he will supply firring strips if you decide to go that way. My guy offers two weights of steel. He recommends the lighter weight for roofs, and the heavier for unsupported walls. I put the heavier weight on my roof for added hail resistance.

It is a couple day job for a couple of guys to install the entire roof. Absolutely NO skilled labor involved. If you can climb the ladder and get on the roof, and are smart enough to not walk off the edge, you can install a steel roof.

One warning, do not attempt to work on steel when it is wet. It gets slicker than snot. Especially with a skiff of snow on top.

Around here, we deal with "Treasure Valley Steel". I bet you have a similar manufacturer in your area. Fire up the old google-fu.

Think outside the box. Build an over-size, free-standing, metal roofed cover for the home to add a covered patio or parking area.

Ice and water shield on an entire roof deck in any climate but yours will result in rotting out your roof in turbo time.

I don't care what the requirement is, or even if there is one.

If I walk around on a shîtty, 20 yr old cooked-out mobile home roof with dry rotted 3/8" plywood on 2ft truss centers. I can assure that wimpy, crunchy 3/8" plywood isnt much of a viable medium to hold a screw driven into in it.

So, thus I "like" and "encourage" people I've done these jobs for opt for horizontal furring of 1x4 spf.

The only way I would go directly back onto bare plywood, would be if the house's attic was well ventilated to begin, the structure was 10 yrs old or less AND it had 1/2" 3ply cdx ply.

Again, check out the plywood, even better if the house rafter are on 16" centers, cover it with 30 or 15. (30 is a personal preference)

For many this is only “thinking outside the box” when taken literally.

If have seen that done too. Which, in the scheme of costs...and it being a camp house like Bobmt reminded us of.

I have a 36ft long steel carport awning over my Jayco. It was $3200 for the mexicanos from Eagle carport to come erect in 6 hours.

Why not?

I see what you mean: install the purlins and remove the decking from the equation. I absolutely wouldnt put new materials on a chitty structure either. My way assumed the decking was inspected and repaired as needed . Thats the correct way instead of leaving chit there and going over the top of it.

Oh yeah, my bad...I only did a couple dozen metal roofing jobs but I've done 500-600 other compete asphalt shingle jobs.

I realize that puts me in the "jackoff of all trades category"

Would've done more but I had a real job being a GIS Analyst for an engineering team the first 8 hours of my day.

Lol..... yes, it can mean he never figured it out, and just moved on, true. But try that when you are working for family. That general contractor is my father, the Engineer.
(And my role model)
My job was to solve problems, keep jobs moving and on time, jump into any job that needed help, and I was good at it. I gave it up to go to college, stepping down to laborer to concentrate on my studies.
I'm still a trouble shooter, a service tech in the trades, and a specialist for more than the last 35 years. But you are welcome to your opinion, sir.

check this out.
https://mobilehomeliving.org/popular-mobile-home-roof-over-materials/

+1

Of course if it were my home I would strip it but for an old mobile home or camp that's a different story since I have seen it done this way on an old camp and it worked well and camp stayed cooler in the summer.

Shingles over shingles was always a bad idea...however tin over shingles is somthing different...I use the roofing tin that has the shingle look...put it right over the old shingles..all the roofing guys I talked to said its not a problem...and I can't think of any reason it won't last..

If you lay metal directly on shingles, it's advised to use felt between them to prevent the granules from scratching the paint off the metal which can promote rust.

After bad hail storm a couple years ago, company that put my metal roof on insisted on tearing the asphalt off. Only took them about 6 hours on a 2000 sq. ft house. My electric bill has dropped considerably in the summer now.

And what was the bill for that six hours? And the bill for disposal of old roofing material? That is the raping I earlier referred to. An absolutely unneeded task, and fee.

Sage advise... Take the time to do it right. It ain't rocket science.