How do you increase the pitch on a flat roof?
Do flat roofs have a pitch?
A flat roof is a roof which is almost level in contrast to the many types of sloped roofs. The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. The National Roofing Contractors Association defines a low-slope roof as having a slope of 3-in-12 or less.
How do you change a flat roof to a sloped roof?
How to Replace a Flat Roof With a Sloped Roof Remove the roofing membrane of the flat roof. A flat roof is easily replaced by a one-way slope or shed roof. Cut rafters to the hypotenuse of the roof plane depth and stud wall height. Apply the polyethylene sheeting and roof underlayment, and place the rolled roofing or shingles.
Can I change a flat roof to a pitched roof?
Simply replacing your existing flat roof with a new one should be a pretty straightforward process. When converting your flat roof into a pitched roof, that’s when planning permission may come into play. A low-pitched roof should be easy enough to gain planning permission for.
Can you change the pitch of your roof?
Changing the pitch of a roof is only possible when a roof’s internal and structural materials are also replaced. When a roof’s ridges, walls and rafters are switched out, there is a chance to create a new architectural design that can change the pitch of the roof.
What is the smallest pitch for a roof?
The smallest pitch of a roof is 1/4:12, which translates to 1/4 inch rise to 12 inches of run. Such a small pitch can only work with built-up roofing or specialized synthetic roofing.
Increase the pitch by building a roof over an existing roof
When your roof needs to be replaced, often you have to have the entire roof removed before you begin to replace it. But if you have an old home with a decaying roof, especially a low-pitched roof, removing the old roof and replacing it may not be practical. In this case, you can build a new roof over the old – with a caveat. You must not build the new roof directly over the old. A new coat of shingles over decaying shingles will cause your roof deck to decay. The solution is changing the roof pitch or building a new roof at a higher pitch than the old roof.
Raise the Roof Pitch
The roof pitch is how much the roof slants. You’re going to want the pitch of your new roof to be steeper than that of the old roof. If you choose a simple trussed roof or addition with two angled planes, that will be the easiest project. And this is a project best saved for dry weather. Before you start, you should have an engineer or architect verify the structural integrity of your home. The cheapest option would be to leave the old roof in place and place the new rafters over the existing roof.
Use Premade Roof Trusses
Premade roofing trusses will be easier and take less time than installing a stick-built roof. Premade trusses will form the skeleton of your new roof above your old roof. Make sure the pitch of the trusses is the pitch that you want for your new roof. A common house roof pitch is 5 by 12, which means it slopes up from the wall at 5 inches per foot.
Things You’ll Remove
You’ll need to remove the siding where it meets the roof. Remove the top several levels to expose the wall. You’ll also need to remove the soffit. Take care if there are any electrical outlets in the soffit. Make sure to disconnect those before starting. Once the soffit is removed, the old roof trusses are exposed.
Installing the New Roof
To provide a framework for the new trusses, nail 2-by-6-inch strips of wood around the perimeter of the roof. Or, if you want to raise the roof a bit more, install fascia around the roof perimeter, attached to the new soffit, and nail the new roof deck to crown molding above the fascia. Make sure you plan all this well in advance so you’re prepared when you do the installation.
If possible, remove any plywood under the old roof, especially if it’s rotting. Also, remove any flashing and air vents by prying out or unscrewing the fasteners that hold in the fixture.
Doing the Heavy Lifting
Once your demolition is complete, you’ll need to set your trusses in place over the existing rafters. To be safe, you’ll need several people to assist you. The trusses should be placed 24 inches apart. Consider that each truss is likely 1 and a half inches wide, so take that into your calculation. To properly install each truss, you will use 2 by 4 wood strips from the ground up to hold the truss in place on each side of the roof. For safety purposes, it’s best to have two people hold the truss in place where it meets the 2 by 4 and one or two people to set the truss upright and fasten it. Use a level to get the truss vertically plumb, and fasten it to the walls through the truss bearing point with framing nails and a hammer.
Once the row of trusses is complete, set a ridge board across the top to connect them from each end. Then nail the trusses to the ridge board. Use a level to make sure the ridge board stays even. To fasten the trusses to the wall caps, use hurricane clips, which are metal brackets that hold the trusses tight to the walls. Do this on both sides.
Steps to Finish the Job
Install flashing at the roof eave and rake using drip edge flashing. Install the eave flashing first, then the rake. These should look neat at the corners. Nail these at the high points of the roof. Install metal flashing where you have air vents, holding it in place with roofing cement. You’ll need to use step flashing around a chimney and protect it with counter flashing. The counter flashing will need to be bent even with the brick design on the chimney and set into place with mortar.
How to Change Your Roof Pitch
There are many reasons for a homeowner to want to change the pitch or slope of a roof. Flat or low-slope roofs may develop leaks because of poor drainage. An existing roof may not provide enough attic space for storage. An addition may look better with a higher pitch on the old part of the house. Whatever the reason, changing the pitch on a roof requires removing at least some of the roofing and a significant alteration will involve changing the basic framing by installing new rafters or trusses. It requires good carpentry and roofing skills.
Flat or Low-Slope
- Alter the pitch on a flat or low-slope roof with some type of rigid foam insulation; at least two different types are made in sloped panels. Remove the existing roof covering down to the underlying wood sheathing. Make sure the sheathing is solid and remove any protruding nails. Repair any broken or water-damaged sheathing.
- Install rigid foam panels with various tapers and thicknesses; insulation panels generally vary from slopes of from 1/8 to 1/2 inch per foot, with sheets butted together to cover the length of the roof. Use a single slope from one end to another or various types of multiple slopes to drain on two or more sides. Fasten tapered panels with adhesive or mechanical fasteners, depending on the manufacturer’s recommendations.
- Put down any required vapor or thermal barriers, according to local building codes. Cover the tapered roof with a membrane such as ethylene propylene diene monomer rubber, thermoplastic olefin or polyvinyl chloride. Make sure metal flashing is properly installed on all roof edges and around any penetrations, such as chimneys or vent pipes.
- Change the pitch on an existing sloped roof by removing the old roof and framing. Take off shingles or other roof covering and remove the membrane and sheathing. Use a pry bar to pull loose shingles and wood decking. Strip the roof to its rafters or trusses.
- Remove rafters or trusses one at a time. Use a pry bar to pull nails loose, then remove them with a crow bar or hammer. Drop old framing down to the ground; get help — don’t try to remove and drop rafter or truss framing alone. Inspect the wall caps once all framing is removed and repair or replace any damaged cap boards.
- Use prefabricated trusses to put a new pitch on the roof. Give the width and length of the roof and a chosen pitch to a truss supplier to build trusses to order. Use at least a 6/12 pitch, rising 6 inches per foot of slope, to provide attic storage; get special attic roof trusses to make a room inside the new roof.
- Raise trusses to the roof, spaced at 24-inch intervals. Fasten them to the wall caps with 16d framing nails and a hammer through the truss ends into the wall caps. Use a level to plumb each truss. Cover truss rafters with oriented strand board, fastened with 8d galvanized nails. Put metal flashing on edges and peaks and any vents or penetrations. Staple on roofing paper and finish with shingles or other roofing.