AboutRon Haynes Expertise I can answer questions related to all types of steep slope and low-slope commercial and residential roofing, including asphalt shingles, metal roofing, built-up roofing (tar and gravel), modified bitumen roofing, single ply roof systems, tile, and slate. Questions may relate to design, installation, problem resolution or repair of the roof system.
Experience I have over twenty years experience as a roof consultant dealing with various types of roof systems on commercial, industrial, residential and Government facilities. Experience includes new roof and reroof design, roof repair specification, roof construction, maintenance, failure investigations, performance analysis, inspections, moisture intrusion surveys and studies, and storm damage assessments. I am a registered professional engineer and a Registered Roof Consultant with the Roof Consultants Institute.
Organizations Roof Consultants Institute
Education/Credentials Bachelors Degree in Civil Engineering
Registered Professional Engineer
Registered Roof Consultant, Roof Consultants Institute Certified Infrared Thermographer
Awards and Honors Award Winner, Large Roof Replacement Design Document Competition at the 1999 Roof Consultants Institute International Convention. Dept of Navy Meritorious Civilian Service Award. Armed Forces Civilian Service Medal.
Question My home is in the Los Angeles, Ca., inland area. It has a pitched 4” in 12” roof that joins to a ¼” in 12” roof. There is a skylight and a chimney on the flat roof. I have different bids and would like your advice to help understand the differences.
1) Difference in 4 ply built up hot roof of 1 layer 25 lb fiberglass base sheet in hot asphalt, 2 layers of 11 lb fiberglass ply in hot asphalt, 1 layer of 72 lb fiberglass cap sheet in hot asphalt to a Class-A torch applied roof system with white top coating to a torch down modified Bitumen
2) Using flashing around the skylight or rolling up the cap sheet around the skylight
3) Using a cricket around the chimney or rolling up the cap sheet around the chimney
4) Pitched roof – using single sheet of 30# felt or using 2 layers of 15# felt
It seems that all bids are just to put a portion of the flat roof about 20” to 24” under the asphalt shingles at the join of the flat and pitched roof. I thought a flashing should be used?
The problem areas on the roof has been at the join of the flat roof to the pitched roof (with stains on the ceiling of the pitched roof) and around the chimney. The chimney area needs to be resealed every couple of years now, but I understand that with a cricket this will not be needed any more.
What are differences in quality, cost, maintenance, number of years to expect roof to last, ease of repairs, etc.? Can someone who does torch down roofs also do built up roofs?
Thank you so much for your help. This is really confusing!
Answer Mario,
1)
Of the three systems you mention, my own preference would be for a torch down modified bitumen roof (with granule surfacing) applied over a modified bitumen base sheet properly fastened to the wood deck. But wait, that is not a system specifically described as one of the options. And that is the first point, make sure you get a full description from the contractor of what he intends to install and how from the deck up to the top surfacing of roof. If he can't explain the whats and whys then he most likely doesn't really know what he is doing.
As for the built-up roof described, it makes for a good roof but is messy to install and will have lingering fumes they may filter into the home for some time. Additionally, I must assume the 72 lb cap sheet to be a granule surfaced roll roofing material which is really a low grade sheet compared to modified bitumen. Unlike modified bitumen roll materials, standard roll roofing is not intended for 1/4" slopes. It instead serves as a surfacing material to protect the underlying plies and asphalt moppings from UV exposure. You can expect the roll roofing to last 10-12 years before it cracks, curls at edges, etc.
The second system mentioned (Class A torch applied with white top coating) appears to allude to a modified bitumen roof membrane which is commonly torch applied, set in hot asphalt, or set in adhesive. However, the number of plies is not noted and there is no mention of base sheet material or attachment. The white top coat reference appears to indicate a smooth, ungranulated cap sheet to which a white 'paint' coating is applied for a "cool" roof effect. However, if the coating is not factory applied to the sheet, normally some weathering of the sheet is recommended prior to coating application to allow oils to bleed off so that the coating properly adheres for long term performane. Otherwise, coating may peel or blister.
The 3rd system, torch down mod bit, only very limitedly descibes the membrane. Is it one ply over a base sheet or 2 plies over base? Or, it the one ply of mod bit applied directly to the wood deck (can you say FIRE!!!)? Is the base sheet a #30 felt or a mod bit sheet. What is the attachment pattern for the base sheet and what type of fasteners are used? Does the mod bit cap have a granule surfacing, or some other surfacing, for UV protection? What is the reinforcing within the mod bit sheet - fiberglass (good) or polyester (better)? One ply of mod bit is a 10-15 year roof, depending on grade of material used, and 2 plies of mod bit is a 20+ year roof.
Will the mod bit membrane manufacturer provide an extended warranty when the material is used on residential construction? What type and extent of warranty will the contractor provide (materials and workmanship of what duration)?
Mod bit roofs are relatively easy to find problems/leaks and can be easily repaired with materials available at the big box home improvement stores.
2)
Skylight - Typically a mod bit membrane is turned up the base of the skylight and fastened. Then a sheet metal counterflashing or rim of skylight overlaps the top edge of the membrane sheet. Fiberglass felts and fiberglass reinforced mod bit membrane may crack when you try to bend to 90 degrees. For this reason, sheet metal flashing may be used in an "L" shape to turn up the base of skylight curb and out onto the roof surface. Then the bottom leg of the "L" is stripped in with the roof materials to seal in watertight manner. However, if not properly and carefully addressed this seal can be a maintenance headache down the road.
3)
Cricket should be used on any penetration through the flat roof that is more than 24" wide and it is a good idea to form a cricket for lesser widths so that water is directed around the penetration rather than being allowed to stand in a line pond on the upslope side. Any transition from horizontal to vertical is a weak area of the roof so prventing water from standing in such areas is recommended.
3a) As for leaks around the chimney. The leaks may be from water infiltrating the chimney skin (masonry, stone, stucco, etc.) thru cracks, mortar voids/separtions, etc., and getting behind flashings at the base of the chimney. A cracked mortar cap or open joints on a sheet metal chimney cover can also allow water into the walls of the chimney and it migrates to the interior. So, you might also have chimney inspected and repaired as necessary. If a masonry or stone chimney, you might also consider a clear water repellent to reduce water absorption potential of the chimney.
4)
For the pitched roof, your local building code may govern here, but normally a #30 felt underlayment is sufficient for a 4:12 slope. Also consider waterproof peel and stick underlayment in any valley areas of the pitched roof. This is cheap insurance for a common problem area.
At the slope transition, due to the 1/4" slope, I would suggest the flat roof materials extend up the slope and NOT be covered with shingles for a distance of 24 inches up from the line of change in slope, and extend the flat roof materials another 18" under the nailed shingle area. Thus a band of 42" of flat roof material extending up the roof slope with the lower 24" exposed and the top 18" covered by the first 3 courses of shingles. If you want shingles in this 24" band for aesthetic reasons, have them cemented in place vs nailed. This will avoid nails in any area of potential ponding water at the transition line. Also, the upper terminating edge of the flat roof materials under the shingles should be tapered and overlapped by shingle underlayment to avoid a linear ridge in the shingles and promote watershedding runoff.
You'll need to look into contractor experience with the system they are installing. Ask for and check references of recent jobs and jobs that are over a year old (problems don't always show up immediately). Some contractors can install a variety of roof types while others specialize (and some simply think they can install a roof type but really can't), so I can't really answer your questions as it relates to a specific contractor being able to install both a built-up and a mod bit roof.
I hope this information is helpful and provides some level of clarity in direction. Good luck!
