new metal roof over old metal roof ?'s

[creamedcorn]

Hi,
I want to try the new metal roof over existing dome metal roof on my mobile home as described in "the manual for mobile home repair." I have rain gutters on already, no overhang or soffit, so i just want the metal to end in the middle of the gutter. I am not understanding how water doesn't back up under the ends of the metal on the long sides of my trailer - like when they get full of ice in winter.

to my understanding i have:
1. top of my old metal roof
2. 1/2" insulation
3. 1x4 furring strips - untreated wood
4. foam inside closure strip
5. new metal sheets

What keeps the water from damaging the furring strip on the edge of the trailer, going past it, the insulation, and the foam closure strip? There are no pictures in the manual to really show what keeps the water out of there. Seems like there needs to be some kind of flashing over the wood and insulation, or ice & water shield, or both? The edge on my roof seems like my most vulnerable part for leaking. Can anyone explain this to me?

[JD]

I think your idea of a drip edge metal over the edge furring strip is a great idea. This would allow you to seal that area up real well. Drip edge metal comes in different sizes. Using the larger size with one 2 1/2" leg should allow you to get down into the gutter. You could also have the edge made custom at hvac suppliers that make roof jacks and hvac vents.

I am not sure how you plan to seal the foam closure strip or if you plan to put a sealant on it at all. If the materials are compatible, maybe Liquid Roof or multiple coats of Ames Research Elastobarrier would work. You would have to refer to the manufacturers or test the material out yourself to be sure it does not melt the foam. I keep both products in stock, so if I knew exactly what foam you are using, I could test it for you.

JMO
JD

[creamedcorn]

Thanks for the response, I'll have to find out about the foam closure strips, cause i feel like they do need to be sealed.

Also, I am having a hard time locally finding the "fan-fold insulation", called for in the manual. The manual did say 4'x8' sheets 1/2" or thicker would work. What kind of insulation is that? What is it made of, and what is it for in this application? At my local lumber store I found 4x8 sheets, 3/4" thick, of something called "white rigid beadfoam". Might this work? I just want to make sure I get an appropriate type. Thanks!

[Rod]

Look through this thread. Domed roof like yours. Drip edge on the perimeter furing strip. True 1x material was used along with 1" foam. 3" of overhang past the drip edge was added. No gutter was used.


https://www.mobilehomerepair.com/phpbb/v ... f=6&t=5174

[JD]

If your local home stores do not have the fanfold insulation, ask the special order desk if they can get it for you. If the store sells vinyl siding, they have ready access to the fanfold stuff. Also you can check with any vinyl siding supplier. This is a common product for them. The fanfold will be the least expensive product as well as the lowest amount of insulation. The 3/4" foam board will work as well. The polystyrene "white bead" foam is OK, but the "polyiso" (Polyisocyanurate) foam board is better. Either product should have some type of membrane laminated to both sides, to make the boards stronger for handling and allow expansion movement without messing up the foam. You do need to use some type of insulator between the two metals. If you use the 1/4" fanfold, you do not need the furring strip framing. If you use thick foam, you will need the furring strips.

Look at Rod's posts (the link above) on these roofs. He is the most experienced forum member I have seen posting on the subject.

Question for Rod. What would think about using nominal size 1x4 (3/4" thick) furring strips along the eave edges with 1" foam panels? I have always felt they give just that little extra pitch at the end of the steel panels. The ribs suck right down through the foam and make for a tight fit at the edge.

JD

[Rod]

To the OP.

JD is on the money with the Polyiso foam. If its in the budget for the better foam then get it. Easier to work with as it is stiffer and will give you an extra point or two on R value. However I would use the furring strip regardless of wether you use fan fold or thicker panels. If you just run the panel it will be hit n miss with getting the fasteners through the metal and into the trusses. The furring strips are run perpendicular to the trusses and fastened at each intersection. We use 3" ring shank nails 2 per intersection slightly cross spiked. Then screw the metal panel to the furring strip. This will also allow you to have a consistant screw pattern.

JMO

JD,

Hey there. I think it would give a little more pitch. The only concern is it is the flat part of the metal that rests on the foam so I would be worried about a wrinkled edge. We screw the eave every 6" adjacent to each rib. Your idea got me thinking though..... the last few inches of the foam panel could be beveled with a razor. Or run the first 12-16" in 3/4" foam as well. It would also have to be done at the 2 short ends of the home as the wood intersects at the 4 cormers of the home.

We could take it one step further and start with 2x material at the peak and progress down to 3/4". This would add about 1" over a 6-7 foot span. almost a 2/12! Of course now the metal wont make the bend and a ridge cap would be needed. This could give some pitch and not add to much weight to our roof design. Given a little more thought it could be possible.

Have a good day

Rod

[creamedcorn]

Hi, The guys selling this type of metal roofing are saying they wouldn't use it for anything less than a 3/12 pitch. Obviously my dome-roof trailer has about a 1/12, and a 0 at the top. Their concern is that water will get under the side seams(long edges of metal where sheets overlap side to side).
You guys have obviously done these before. Have you ever had this problem, and would putting plastic, or roofing felt down under the metal be enough to control any damage that a small amount(i imagine) of snow-melt water would cause? Or an idea of a very thin strip of closed cell foam that one could put along these seams to seal them. I would think caulk wouldn't last long, and really what i am trying to avoid anyway- repatching the *%#@** roof every year!
Thanks for all the advice!

[Rod]

The product we typically used is recommended for 2/12 and greater. I have been using it on domed roods for years with out any trouble. make sure you get a panel with a low profile rib. Half inch is perfect for this application anything taller and the metal will not form as well to the dome. The ribs will wrinkle for sure.

Rod