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Building a new roof for a mobile home

building a proper roof for our trailer

We've been having problems with our roof leaking ever since someone gave us this trailer about 6 years ago.

I can't count how many times I "fixed" a leak with roofing tar only to have it come back in a few years.

The new trailer roof project will not only take care of that problem but will cut back on wood burned and split with the extra insulation we plan to install. Trailersteading

Edited to add:

Learn more about insulating and improving the efficiency of a mobile home in
Trailersteading.  Now available on Amazon.

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Roof insulation works best when it has an inch of ventilated air space above it. If that is not possible, use extruded polystyrene insulation (available at Home Depot as 2"x4'x8' foam boards).
Comment by Errol Mon Sep 3 16:06:02 2012
Looks like a good investment for the coming winter. May it keep you warm and dry!
Comment by Roland_Smith Mon Sep 3 16:18:44 2012

Daddy --- We're laying the insulation directly on the roof of the trailer, so the stuff on the very edges won't have air space above it, but most of it will. I priced the foam insulation, but it would cost about five times as much to get the same R value....

Roland --- We agree! We're very much looking forward to no buckets collecting drips of water in the hall. :-)

Comment by anna Mon Sep 3 18:06:57 2012

Roland --- By the way, can you check my math? It's been a long time since high school geometry and I honestly barely remember how to mess with angles. If I want a roof overhang to cast shade on the wall 5 feet below it when the sun is at its solstice peak (80 degrees), would I do:

tan 10 = x/60

x = 11

(Where x is the length of the overhang past the wall)

Comment by anna Mon Sep 3 18:14:54 2012

If I correctly understand what you mean (and assuming for simplicity that the roof overhang is horizontal), then;

Our assumption is a right angle between the vertical wall of the house (which has a shadow length of 5 ft) and the overhang which has a length x. The sunbeam that just grazes the edge of the roof is the hypotenuse. In terms of the catheti, the overhang is c2, and the shadow length ic c1. The angle between c1 and the hypotenuse is 10 degrees. The tangent in this case is c2/c1 or x/5;

x/5 = tan(10°) → x = 5·tan(10°) = 0.88 ft.

Comment by Roland_Smith Mon Sep 3 19:05:28 2012
Roland --- Thanks! That matches up with my math, so I'm going to assume we're right. :-) (Of course, there's a lot of debate on the internet about what time of year to use for your sun angle calculations, but I figure this will do.)
Comment by anna Mon Sep 3 19:33:47 2012
What you could to is fit some strips of wood (or drawer slides if you want to be fancy) on the sides of adjacent joists above the windows. Then put a sheet of waterproof coated plywood between the joists (fitting it on the strips of wood or on the drawer slides but above the insulation). That would give you shades that you could extend or retract as needed.
Comment by Roland_Smith Mon Sep 3 19:49:08 2012
I rented a mobile home about 20 years ago that had a roof added to the top of it. It was rather odd looking, but I can tell you that there were no leaks. The roof itself was supported by 4 x 4s every 8 - 10 feet and they were snugged up against the trailer. We live in North Central Texas where the spring storms begin sometime in February or March and end about the end of June. One March night we had a series of thunderstorms "train" over us for about four hours and the trailer never moved an inch throughout the whole ordeal. I wish you the best of luck in your endeavor - though we know it's more skill than luck!
Comment by Patti Smith Mon Sep 3 20:01:21 2012
Hi, I found a company that sell reclaim ridge foam boards of all different sizes. They have warehouses all over New England stocked with them from commercial building reno's. Theres other companies across the country that do the same. Next project do some homework looking for one in your area. Prices are dirty cheap. 4" 4x8 goes for $5.80. That's an r-24 rates board.
Comment by Marco Tue Sep 4 09:57:27 2012

Roland --- Another possibility is to plant a fast-growing vine along the south-facing windows --- it would block summer sun but only some winter sun. I'm still pondering the best option, but I figure I'll do a moderate overhang to block the worst of the summer sun and then deal with hot autumn sun with something more removable/seasonal so we don't lose the spring sun.

Patti --- Glad to hear your roofed trailer was so snug! We thought we'd have to support the roof with 4X4s, but Bradley seemed to think we'd be okay just adding the roof on top of the trailer. If we see problems, we'll just call him back and prop it all up. :-)

Marco --- Wow, that's extremely cheap. I'm jealous! Are you sure a 4 inch thick sheet is R-24, though? According to the Lowes website, a two inch sheet has an R value of 7.7, which would suggest a 4 inch sheet is 15.4. Still a good deal either way, though....

Comment by anna Tue Sep 4 12:44:10 2012
There are 3 different types of Ridge foam insulation. That particular type is Polyisocyanurate, or ISO board. It ranges in R value from 6-8 per inch. It's also paper faced on both sides so it doesn't lose much R value over time to UV. What lowes and home depot carry is Expanded polystyrene which is around R3.5 per inch.
Comment by Marco Tue Sep 4 22:10:37 2012
Marco --- Thanks for the followup! That makes a lot of sense, and would explain why I hear such different R values per inch when folks talk about foam insulation.
Comment by anna Wed Sep 5 07:18:18 2012

Polyisocyanurate (also known as PIR) is much less flammable that polystyrene if a suitable unflammable blowing agent is used.

Neverthless, keep some distance between the isolation foam and your chimney, and fill that with some inflammable insolation like rockwool.

Comment by Roland_Smith Wed Sep 5 16:15:24 2012
Roland --- Luckily, our wood stove is in a little addition, so we don't have to deal with roofing over it again. We bought a special ceiling support kit to ensure the chimney went through the roof without burning anything up. Good to know that we could have used rockwool in there, though!
Comment by anna Wed Sep 5 20:11:02 2012

Many, many people build a roof over their mobile homes in North Idaho to help with the snow load, but if I recall correctly they install the roof on posts that are imbedded in concrete. This keeps the weight off of the mobile roof and of course, saves the roof from leaks and damage.

Here's to drier days ahead! :)

Comment by Dawn Thu Sep 6 11:31:42 2012
Dawn --- I've seen roofs added to mobile homes with and without the four by four supports. Since we live in an area that seldom has heavy snow loads, we opted for the without version, but I'll be sure to post if we have problems. :-)
Comment by anna Thu Sep 6 14:19:46 2012
If I understand where you live, Knoxville might offer guidance on snow loads. The record 24 hour snow fall in Knoxville was 18.2" November 21-22, 1952. I am not sure about elevations in that area, but if Knoxville is at a higher ellevation, that would tend to increase snow fall.
Comment by Gerry Thu Oct 25 14:20:56 2012
Hi. We will be doing an addition on our mobile home this summer. It currently is 16x68. Our mobile home has vaulted ceilings. We are looking to make it 30x68. This past summer we moved the home on to a cement slab we poured.Our goal is that when we are done it does not look like an addition inside and out. Does anyone have any ideas about the best and most inexpensive way to go about doing this? We are doing all the work our selves and have a lot of knowledge in everything. Expert in nothing. Would love any suggestions!!
Comment by Michelle Mon Jan 28 09:47:39 2013
I was wondering how this new roof was attached to the mobile home roof? I am going to be doing this next year and I would like to know how it is done.
Comment by Ray Thu Jul 23 15:24:44 2015
Hi,i just came across your site.I seen where you built a new roof over your old roof.I have plans to do the same thing in late September.The only concerns I have is whether to take the old roof off before installing the new one.I was told it was create a moisture situation and the roof screws would pull off from the furring strips.Also did you add piers or supports to the outer walls for the added weight of the roof?My original roof is 2 x 2 metal plate together roof trusses.I have pretty much redone my 1987 singlewide except for the roof.Ive cool sealed it.The cool seal works but there is tears in the roofing"30 years old".Its time for a new roof.any help or advice would be great.I live in east tn
Comment by Robert Thu Aug 6 09:11:09 2015
I'm planning on building a trailer roof too, for a 40' home, and have done some research. I read that OUTSIDE POSTS ARE BEST, because trailers have only 2X2's for their walls, and the new roof's weight will cause them to BOW. SO DO THE POSTS !! HOWEVER, DO YOU DO THEM AS ATTACHED TO THE TRAILER SIDES OR SEPARATED from them. WELL, trailer homes do settle, don't they? So best is to keep these 4x4's independent. This likely means placing them upon cement piers for immovability. THESE COST MONEY to make !!! The cement form = $10, cement about $30,4x4 posts = $10+ each, the MOUNTING BRACKET for the post = $12++, and figuring one post every whatever distance, one can rack up a pretty good bill. Intermediate posts CAN be placed without these piers, however, I figure: just stand them up on cement blocks. A single slant roof is easier than a peak roof.
Comment by terry mulligan Mon Jan 16 20:39:58 2017
Dig holes so that posts will fit tight against building wall. Fasten posts to wall for greater strength. Before placing post in hole, add spikes or large screws so they will be below ground level. Fill hole with concrete and allow to set. Mix the concrete, don't put it in dry. A large bag of sacrete should fill one or two holes. Fill remaining hole, if any, with dirt. Holes should be two feet deep, when possible.
Comment by Errol Tue Jan 17 17:16:26 2017