Q: I have received proposals for re-roof of my house however each proposal calls for different underlayments with significant price differences. I live in Southeast Florida. I would appreciate guidance as to what makes the most sense. Thank you for your input; it is greatly appreciated!
– Install on Roof Deck Area: 2.1 One layer of 30# ASTM D-226 asphalt saturated organic felt tin capped to sheathing; New 26 galvanized 2×2 drip edge, vent and valley metal flashing; and new roof vents (GNV);
-One layer of 90# ASTM D249 mineral surface tile underlayment set in a mopping of ASTM D312 Type IV hot asphalt; NO PEEL N STICK!
-Standard color cement tile with ICP AH-160 PolyPro foam adhesive; NO NAIL PENETRATIONS!
– Install on Flat Roof Area: One layer of 75# asphalt saturated base sheet tin capped to sheathing; One layer of fiberglass sheet set in hot asphalt (ASTM D312 Type IV); One layer of CertainTeed GMS modified bitumen (white mineral surface) set in hot asphalt (ASTM D312 Type IV);
Option: add’l $4,500 – GMS Modified: Superior tile underlayment
2nd option: add’l $3,100: Seam Tape: Secondary Water Barrier (SWB)
Proposal 2: (cost is about $8,000 more than proposal 1):
– Install 1-#30 ASTM Roof Membrane mechanically fastened
– Install one layer of self-adhering modified bitumen membrane tile underlayment.
– Install cement color thru roofing tile, (roll style, standards colors) using 2-part polyfoam adhesive
– Flat deck roof area shall receive 1 #75 ASTM extra thick base sheet membrane mechanically fastened
Proposal 3: (cost is $12,000 more than Proposal 1):
– Dry in all roof areas with 30# ASTM base sheet.
– Install standard GALVANIZED 2×2 eave drip, valley, and Inspect & Re-Use Existing wall flashings.
– Install Self Adhering Tile Underlayment to all pitch roof areas and 2 layers in valleys for UV exposure via weave installation.
– FLAT ROOFS/WOOD DECK: Install self adhered 3-Ply Modified Bitumen System
– All field roof tiles fastened with ICP FOAM ADHESIVE and hip/ridge caps fastened with approved adhesive
A: The Florida State Building Code, and the added requirements in Miami-Dade and Broward Counties, are about the toughest in the US when it comes to roofing. Also they have changed the code a couple of times in recent years, getting much tougher in 2002 after Hurricane Andrew, and then revised further in 2007. Florida codes are most stringent in areas subject hurricane-forced winds and flying debris, so-called High Velocity Hurricane Zones.
To meet the current code, roofs must use an approved underlayment system, which Florida calls a Secondary Water Barrier or Secondary Water Resistant (SWR) barrier.
However, not all code-approved systems meet the requirements of the insurance industry, under the guidelines of the Florida Office of Insurance Regulation. To qualify for an SWR discount on your homeowner’s insurance, you must use either a peel-and-stick membrane bonded directly to the roof sheathing (option A below), or a special type of closed-cell foam sprayed to the underside of the sheathing. Also, you must have good documentation, such as a signed contract, that you used an approved system. Installation photos are also a good idea since most of the work is hidden.
The goal in all this is to create a waterproof layer that seals around nails and will stay in place if high winds blow off a section of the roof covering. An intact underlayment keeps water out of the house and helps prevent penetration of the roof structure. Once the structure is penetrated, catastrophic wind damage often follows. The main underlayment options listed in the code are:
A) an approved peel-and-stick membrane adhered directly to the roof sheathing
B) an approved peel-and-stick membrane adhered to roofing felt, mechanically fastened to the roof sheathing
C) minimum 4-inch wide peel-and-stick tape over all seams in the roof sheathing, covered by an approved underlayment (ASTM #30 felt or an approved synthetic)
D) a mechanically fastened base sheet covered with a hot-mop cap sheet.
All of these make sense to me except for Option B. To get the full benefit of peel-and-stick membrane, it needs to be bonded directly to the roof deck. The only benefit of placing it over a layer of felt is that it is easier to remove 20-30 years later when reroofing. Also, Option C is suspect unless you are using a weatherproof sheathing such as the Zip System.
All of your proposals meet the building code, but not all meet the requirements of the insurance industry. In particular, Proposal #2 seems to place the peel-and-stick membrane above the base sheet.
It sounds like your roof contains both flat and sloped sections, which are handled differently in these quotes. There are a lot of moving parts here, so apples-to-apples comparisons are difficult. Also, there are dozens, if not hundreds, of underlayment systems on the market now and many use proprietary materials. Most synthetic and modified-bitumen (rubberized asphalt) products do not have national standards, adding to the difficulty in comparing products.
Two of your proposals fasten the tiles with foam adhesive. In general, two-part foam adhesives, like the one proposed, provide better hold-down strength than nails or screws. It also eliminates nail holes in the underlayment and provides a cushion that helps prevent tile breakage from walking on the roof. One-part foams are sometimes combined with nails or screws for a hybrid approach with similar performance at less cost.
So let’s break it down:
Proposal 1 is a hot-mop system with all new flashings and two-part foam tile attachment. Hot mop underlayment is the traditional approach in Florida. If done well, these systems are durable and easy to repair if a leak forms. However, a high-quality peel-and-stick underlayment will probably outlast hot mop. The option for a white mineral surface on the flat portion might increase its longevity (compared to standard hot mop) and should reduce your cooling load somewhat. Adding seam tape is a belt-and-suspenders approach. However, if water has reached the wood sheathing layer, I don’t think the tape will provide much benefit as you can expect delamination or decay in the wood and failure of the tape. Also, peel-and-stick in the valleys would be a worthwhile addition to this approach.
Proposal 2 places the peel-and-stick membrane over the base sheet. I’m not a big fan of this approach, and neither is the Florida insurance industry as far as I know. Also, it’s not clear what the top layer (cap sheet) is on the flat area. Standard peel-and-stick is not a roofing surface as it will degrade under long-term exposure to UV.
Proposal 3 uses self-adhered underlayment (good), double layers in the valleys (very good) and a 3-ply self-adhered system of the flat areas. The flat area uses one of many newer systems competing for the flat roof market. I’m not sure exactly what this is, but would want more information on the system, manufacturer, guarantee, and track record. How long has it been on the market and how many roofs has the contractor installed? What does he like about the system? Any downsides? Also, this proposal wants to re-use wall flashings. Unless they are in excellent condition, this is risky. However, they can be expensive to replace in a stucco wall.
For my money, the best material for flat and low-slope roofs is EPDM. Done properly, it will far outlast any other material – typically 40 years or longer. PVC has similar characteristics but is less commonly used on residential projects.
Finally, with any roofing product and system, the installation is at least as important as the materials. So choose an experienced contractor with a sterling reputation, a long track record in the area, and a strong written warranty. For the most part, you won’t see the little details that make the difference between a 10-year and 20+ year roof.
– Steve Bliss, BuildingAdvisor.com