One or more test cuts can determine the materials and deck type. Most low slope roofs have the insulation immediately above the deck and the waterproofing layer on top of the insulation. Sometimes there are multiple layers of roofing systems. The deck type usually can be determined from underneath (you may have to pop a few ceiling panels). See our test cut page for examples of what different material looks like. Anyone can cut into a roof but most roofs need to be patched by a professional. For example – asphalt based patching products are chemically incompatible with most single ply membranes.
The no risk, high dollar approach is to rip off everything, inspect and replace damaged decking, then go back with whatever roofing system you choose. This option is favored by many roof consultants and roofers as they are guaranteed there is no moisture remaining in the roofing or damage to the deck. Under certain conditions this is the proper approach. Under other conditions this is wasteful of the owner’s resources and un-friendly to the environment. Removing the roofing to the deck incurs larger costs for the labor and disposal of the old roofing material as well as the usual installation of thicker insulation to meet your state’s building code.
If the deck is visible from underneath that is the first place to check. Rust, flakes, soft spots, sagging, discoloration all point to deck problems. The other way to check is through test cuts. Take a 2′ x 2′ test cut and examine the deck. Some deck issues like rust will not show up from the bottom until too late. Examining the deck from above takes some experience. Metal decks should be inspected for rust and poked with some gusto to make sure the metal is solid. Wood decks should be poked also to make sure they are solid. Concrete decks are trickier. Some concrete decks utilize lightweight concrete or gypsum to provide the slope in roof. Some roof decks are completely lightweight concrete or gypsum. There are some very strange combinations of materials on some older buildings. Once in a while ponding on a roof can point to deck problems (usually the problem lies within the roofing system).
If there are major deck problems the entire roof should be removed and the deck issues addressed. If there is a small area with problems it may be cost effective to only remove the roofing in that area, replace or repair the decking, then install new roofing material to the height of the adjacent roof area. If the condition of the deck is suspect and the new roofing system you choose utilizes mechanical fasteners (or adhesive directly on the deck) to secure either the insulation or waterproofing layer a pull test should be done. This involves screwing a fastener into the deck and utilizing equipment that measures the force (lbs.) required as it pulls the fastener straight out of the deck. The roofing manufacturer of your intended system should be able to perform the test and tell you what length warranty is available based on the test. The same principal applies to a pull test with adhesive. A pull test is especially important for metal roof go overs. The pull test also may help decide the fastening pattern required to meet certain wind uplift scenarios.
Moisture in the roofing system is bad. It attacks a roofing system in many ways. It works its way down to rust or rot the deck. It turns into gas when heated and attacks the seams, penetrations and other weak spots trying to escape and causes earlier failure. It freezes in the cold and lowers the thermal resistance, increasing heating costs. The freeze/thaw can cause excessive shifting of the waterproofing layer causing earlier failure. If moisture is in a roofing system it should be removed. However, a cost saving approach can be taken to remove just the layer or area that contains the moisture.
The answer to this depends on how many and what type of roofing system you have. Test cuts can be done at different spots on the roof. This is the only certain way to tell if there is moisture in the roofing system(s). Test cuts should be done anyways to determine the make-up of the roofing system(s). Since water runs downhill, test cuts should be taken near drains and gutters, as these areas are the most likely to contain moisture. Test cuts by themselves don’t pinpoint the exact wet areas. For that a moisture scan is needed. We are familiar with two main types – the nuclear scan and infra-red scan. Infra-red scans are done in the early evening as the air temperature cools down. Any wet areas in the roof will retain heat longer than the surrounding areas and an infra-red camera can pick up the thermal differences. A nuclear scan can be done at any time of day. To do the nuclear scan the roof is sectioned off into an imaginary grid, usually 10′ x 10′, and at each intersection point the device is placed on the roof and a reading is taken. The higher the reading the more likely moisture exists. Both moisture scans should be confirmed with test cuts.
Test cuts need to be patched properly to last. Materials similar to the to the roof’s waterproof layer need to be used (asphalt cannot be used on rubber, etc.) and any asphalt patches should use embedded fiberglass mesh. Plastic based membranes (TPO, PVC) should have the seams of the patch heat welded. If the roofing system is under warranty it is usually a requirement to have certain qualified contractors do any work (check the warranty language). The infra-red and nuclear tests have their limitations. The infra-red, which is the least expensive and easiest, does not work well on ballasted single ply systems or show moisture well in anything but the top roofing system if there is more than one. The nuclear is more labor intensive hence costs more. If there are multiple roofing systems then utilizing both provides the most accurate reading.
Any wet roofing materials need to be removed and if those wet materials are next to the deck then the deck needs to be inspected for damage and repaired, overlaid with new decking or replaced. With that stated the issue is whether just the wet materials be replaced or does the entire system(s) need to be removed. While there are some other considerations that will require the complete roof removal (addressed later), it really boils to down cost. Figure out which type of new roofing system you want to use then obtain a price to install this new roofing system as a “go over” by replacing all wet areas with insulation of a thickness that matches the height of the surrounding area with a new system installed on top of the old. Then obtain a price to remove the entire roofing system(s) and install a new roof system. If the difference between the “go over” and complete replacement to you is substantial, just replace the wet areas and install the new roofing system over the old. If the difference to you is not substantial – go with the complete removal of the existing system(s).
Maybe. There is a difference of opinion in the roofing industry about the efficiency of vents drying flat roofs. Roofing systems for flat roofs are designed to stop water from coming into a building and further to provide energy savings through insulation. Minor consideration is given to what happens within the roofing system if the waterproofing layer fails. To keep the roofing system in place during high winds the layers of roofing are bound tightly together with no air flow. The lack of air flow inhibits the performance of a vent. Vents installed in the field of the roof will provide a path for some moisture to escape. Will this percentage of moisture escaping be meaningful? Depends on how many vents, how many roofing layers and if the leaks causing the moisture were stopped. If the roofing system is a single-ply membrane and the attachment method of the membrane is with bars/plates instead of adhesive, vents become much more effective, and in some cases two way vents will assist in securing the membrane to the roof.
If there is no moisture in the roofing systems and none of the previously stated conditions exist that would dictate a complete removal of both systems, the next step is to check with the town building inspector. Does the building code limit the number of roofing systems? Typically no more than 2 roofing systems can be used. There are times when the building inspector may not consider the addition of another waterproofing layer (single ply membrane or coating) to be a 3rd roofing system. Check and make sure. The top roofing system can be removed in its entirety and a new system can be installed on top of the bottom roofing system. If it is possible to remove just the waterproofing layer of the top roofing system and leave the top roofing system’s insulation in place then attempt to do that as it saves on removal and disposal costs as well as future energy costs. Most of the time removing the waterproofing layer will cause some damage to the insulation underneath and something should be placed on top of the old insulation to provide a sound substrate for the waterproofing layer. This usually is another thin layer of insulation or a manufactured board like DensDeck. Check with the manufacturer of the roofing system to be installed as to their requirements (which may change depending on the length of the warranty being requested).
If there is no moisture in the roofing system and none of the previously stated conditions exist that would dictate a complete removal of the system then just check the waterproofing layer. Can the waterproofing layer be left in place? If it is a single-ply membrane then most manufacturers allow the membrane to be left in place providing it has no contaminates (oil/grease) and is sliced into a 10′ x 10′ grid. The two explanations we have heard for slicing the membrane are that it either relieves the tension in the system or it prevents a vapor barrier from being in the middle of the roofing system. (Side note: we have seen a few instances where a polyethylene vapor barrier was actually placed on top of an existing roof and new insulation/membrane installed above. This invariably kept the bottom roofing system drier and even prevented water leaking on the tenants, but spread the moisture throughout the top roofing system – likely causing it to fail sooner.)
If the single-ply waterproofing layer cannot be left in place or sliced and left in place then it should be removed. If the system is asphalt based without gravel (modified bitumen or bald asphalt) then usually no extra measures need be taken – another roof can be placed on top. If the system is asphalt based with gravel (asphalt/tar/pitch and gravel) then the gravel should probably be removed. We have seen many roofing systems where the gravel was left in place, insulation mechanically fastened and EPDM installed, with no adverse effects. We have seen a few instances where the same scenario produced tenting fasteners – but it is hard to say if the fasteners tented due to a poor roof deck, water in the bottom roofing system or the gravel shifting a little as time went on. If a second roofing system is being put in adhesive over an existing roof with gravel then the gravel and dirt must be wet vacuumed off to obtain a good bond.