Flat to pitched roofs and typical ventilation issues.
The life expectancy of tar & gravel roofs
Also look for tar blisters. Cover them with a coat of bitumen and pea gravel. Look for ridging and buckling of the felts. Little can be done about this except to cover these areas with more gravel top make them less obvious. If water ponds in areas of the roof the felts will deteriorate more rapidly in these areas because the freeze / thaw cycles affect felt life. Note the low spots. If small in size you can fill them with bitumen and re-gravel or consider re-sloping these areas when the roofing materials are replaced. Other problems such as felt slippage, flashing failures and “fishmouths” can be repaired but should be referred to a qualified tar & gravel roofing contractor.
Water stains inside house caused by ice build-up in eaves
When the liquid behind the ice dam backs up the water often find its way under the shingles. This usually happens directly above the outside walls because the warm air escaping from your attic keeps the melting snow water in a liquid state. This water can now find its way down into the outside wall cavities. In turn, the water will often appear as stains near the top of exterior walls on either the inside or outside of the walls.
Some folks resort to a quick and simple answer to the problem. They install heat tape along the eaves of the roof. This melts the ice dams eliminating the potential for water build-up behind the ice dams. But this solution does not address the fundamental problems. Here are some suggestions for eliminating the problem.
First, go up in your attic and remove any insulation in contact with the underside of the roof deck. You can also install insulation baffles that will help hold the insulation down and away from the deck of the roof at the rafter junctions with the outside walls. If you have little or no attic ventilation through your soffits, gable ends and at the ridge of your roof, definitely install more of each. Then go outside. With a ladder on your roof eaves lift up the first course of shingles at the eaves. There should be one or two layers of felt paper under the shingles (dampproofing). This dampproof layer is the last line of defense against ice damming. It is installed to at least one foot above the outside wall of your home and its purpose is to help carry off water that may build up under shingles from ice damming. If you don’t have a layer of dampproofing felt you don’t have the final line of defense. Correct the insulation and ventilation problems first and the next time you install new shingles install the dampproof course at all the building eaves.
Roof tar hard, starting to crack and flake
For instance, the metal on mobile home roofs have mechanically sealed seams between sheets to provide additional protection from leaks due to movement (in transit / seasonal shifting) and the low pitch design of the roof. Often, the metal is fastened to the eaves of the home, providing some structural rigidity for the exterior walls to which the roofing is fastened. These seams can lose their seals, so when you are caulking and re-sealing the other flashing details, you should consider re-sealing all these metal seams as well.
The most common material used for re-sealing flashing penetrations and metal seams on mobile homes is a silver coloured metal paint sealer that is available in 4 litre containers from your local travel trailer / camper retail sales business. However, it seems that someone has already re-sealed your penetration flashings with tar, which has now cracked and deteriorated. So, you should scrape and remove as much of this old tar as you can from around all the flashings. Then clean the metal surfaces with a petroleum distillate. If the metal is clean and free of all tar you can re-seal the flashings with the metal paint sealer. If you can’t get all the old tar off, then re-seal the flashings with a soft tar roof patching material. This product is available at any building supply and most hardware stores. If the metal roofing does not have any sheathing under it, lay a 4’ x 4” piece of plywood down in the areas where you are working so you don’t buckle the metal roofing. Because metal roofs on mobile homes are structurally rigid and flexing due to seasonal temperature changes, you should check all the seams and flashings annually and be prepared to re-seal them in spots as required. The only alternative to this regular maintenance is to consider constructing a snow roof over the length of your home.
From your description it seems that the roofing didn’t include a tarred “breather paper” on top of the 1×4 strapping, under the metal roofing sheets. This paper has one-way breathing characteristics, allowing moisture from the warm garage / shop air to flow through the paper, condense on the underside of the metal and drip onto the topside of the paper. This “ breather paper” ensures that this condensation will not return into the building envelope. If it is not installed under the metal, you can expect that this condensation will continue to occur whenever certain interior / exterior temperatures and building humidity levels converge to create a dew point on the underside of the metal. Unfortunately, the only solution will be to remove the metal and install this breather paper under the roofing. Then you are just left with the possibility of occasional leaks from water seepage that may also be mitigated by this breather paper.
Leaky, moss-covered roof
In my opinion, the best replacement product for a low pitch roof is a material called “torch-on” or “torch-down” two-ply membrane. Unfortunately, it is expensive (about $6.00 per square foot) and requires a professional roofer for a guaranteed, quality installation. However, for garages, patios, carports, outbuildings and habitable areas if you cannot afford “torch-on” roofing, you may consider a new, less expensive alternative called HR Cap Sheet. This is a one-ply “peel & stick”, self-adhesive, elastomeric product that can be installed by a skilled homeowner on roofs with slopes greater than 1 in 12. You will have to strip the old roofing off and prepare the bare roof deck as directed. The product comes in a variety of colours, and it has a 15 year warranty against manufacturer’s defects. So, be sure to follow all the manufacturer’s installation instructions or hire a qualified roofing contractor to help you with the installation. Most building supply stores carry this product or an equivalent material.
Proprietary roof shingles
For instance, your metal shingles will have a unique profile and a unique way of interlocking with all the adjacent shingles. The beauty of this uniqueness is that the manufacturer probably designed an amazingly well sealed roofing system. As a matter of fact, metal roof shingles have a great reputation for durability and performance in the construction industry. However, the downside of these proprietary systems is that it can be very difficult to find parts when damage occurs and shingle replacement is required. It becomes even more difficult when the manufacturer of the system has gone out of business, which is the case with some of the better known metal, sawdust composite and rubber roof shingle manufacturers.
So, I suggest that you try to determine the brand name of the shingles. Then, do a building supply store and “Google” search for the manufacturer. If the company is still in business, make contact with them for replacement shingles. If the company no longer exists, your last resort is to find a skilled sheet metal tradesperson to attempt a duplicate copy of your shingles. You may anticipate higher than expected costs for this work because it will be a small, labour intensive job that most tradespeople prefer to avoid.
Rafter lines visible through snow covered roofs
This thermal transfer or “thermal bridging” as it is called in the construction industry, is the reason it has become very popular to construct double staggered stud exterior wall cavities in new home construction. In other words, modern home builders, looking for energy efficiency often build “staggered stud” exterior walls ( 2″x4″ studs offset on a 2″x8″ or 2″x10″ plates) so no wall studs directly contact both the interior and exterior wall surfaces. This staggered stud construction has the added benefits of creating significantly more insulation space and subsequent superior sound control in a wall cavity than a conventional 2″x6″ framed wall. The additional costs in materials are quickly recouped in heat savings and personal comfort from reduced noise transfer through the exterior walls.
Deck as a roof
The installation of fiberglass requires mixing components that cure and harden over time. If the ratios of components vary from batch to batch or from one installer to another, the ability of the fiberglass to resist water penetration will also vary. As well, the surface gel coat is the real sealer. This is a micro-thin film on the surface of the fiberglass. If this veneer cracks due to deck movement or it is damaged by chairs or foot traffic, your waterproof seal is lost. This is the most likely reason your original deck leaked.
Roll roofing, your second choice, is a recognized roofing material, but it does not work well in flat or low slope applications because the narrow, tarred seams are vulnerable to water penetration. On moderate or steep pitched roofs these seams are well drained. But, in the long term, they will not resist standing water in a flat or low pitch application.
For a short term repair to help seal your existing deck leaks, you may try applying a concrete sealer to the surface of the concrete. But long term solutions will be costly. You may consider installing 60 mil vinyl decking over a new plywood layer installed over the existing concrete. If you like the appearance and feel of your existing concrete topping, you may be faced with removing this concrete and roll roofing under it. Then install either a torch-on or EDPM roofing membrane. Before you cast the new concrete topping, check with the manufacturer of the roofing product you have chosen. Be sure the manufacturer warrants their product for use under a concrete topping. You may find that the manufacturer will want their product to be accessible for future repairs. This means that you may have to install removable pre-cast concrete pavers over the roofing material you choose. Research these options thoroughly with installers and product manufacturers before making a final choice. Whichever of these product you choose, try to incorporate a slope to the outside edge of your deck. All roofing materials last years longer if they are not subjected to the freeze / thaw cycles of ponded water.
Mould and mildew in old attics
Once insulation was introduced to this space, it sealed and separated the attic from the living area below. Nobody considered that the attic had to breathe, so it morphed into a hot and often humid area, full of trapped dead air. To compound the problem, a vapour barrier is often mistakenly omitted when older attics are insulated. So, the humidity from the hot humid interior air condenses on the roof boards because it is not prevented from entering the attic by a vapour barrier. Fortunately, sometimes the ceilings of older houses are well sealed with layers of old oil based paints. These layers of paint often save old attics that have been retrofitted with insulation, from the mould you are now dealing with.
The key to the whole problem is to introduce lots of fresh circulating outdoor air through your attic. Unfortunately, most older homes do not have soffit vents. However, you can easily install manufactured round soffit vents in drilled holes. These soffit vent plugs are readily available at you local building supply store. Install 38mm vent plugs on 300 mm centers. More is always better than less when it comes to attic venting. Before you are install the new insulation, ensure these vent plugs allow air flow into the attic by installing insulation baffles (“mor vents”) between each rafter bay in the attic. Then, install large gable end vents. These vents allow the fresh air drawn through the soffits to escape and carry off any heat and moisture that could provide an environment for mould growth in your attic. Then, it may not be critical to attempt a lengthy clean up of the existing mould. Without a hot humid environment the existing mould will no longer flourish.
When working in your attic, be careful not to disturb the vermiculite insulation because it may contain traces of asbestos. Wear a good quality respirator and leave your shoes and coveralls in the attic before you come back into the living area to avoid the potential for transfer of contaminants to your living quarters.
Lack of roof venting and poorly installed insulation
For instance, you mentioned that the previous owner had re-insulated the old attic space when he installed new shingles. One of the most common mistakes when re-insulating is to carelessly fill the horizontal ceiling structure. It is fine to add six, twelve or even fifteen inches of additional insulation to an attic that had little or none. However, care must be taken to ensure that the old and new insulation does not come in contact with the underside of the roof deck at the outside walls.
This insulation / roof deck contact surface will transfer heat from your house directly to the asphalt shingles causing them to expand and contract (“cycle”) significantly more than they were designed to withstand. As well, the insulation is blocking the incoming air flow through the soffits into the attic. This creates a hot and possibly humid attic space which leads to mould, mildew and another reason for a decrease in shingle life expectancy.
Fortunately, your shingles are still new enough to warrant saving. Here’s what you can do. Measure the distance between your rafters. Then purchase from your local building supply store one appropriately sized cardboard or styro-foam insulation baffle for each space between your rafters. (I prefer the cardboard baffles because they hold the insulation further away from the underside of the roof deck). Then, you may need to drill holes in your soffits and install soffit vent grills if your soffits have no vents. This will let air into the attic through the newly installed baffles. Also, install large gable end vents or some form of “top of roof” venting such as turbines, passive air vents or continuous ridge venting to provide the incoming soffit air with an exit at the top of the roof.
“Blistering” problem with tar and gravel roofing
In both tar and gravel and torch-on roofing, the blistering is caused by delaminating between the plies or layers of roofing felts or sheets. In tar and gravel applications this can happen because the “mopped on” tar layer between the felts was too cold or poorly applied. With torch-on roofing the reasons for blistering are different, but the end problems similar.
When torch-on roofing was becoming popular as an alternative to tar and gravel roofing some 15 years ago, the manufacturers hadn’t perfected the way the removable plastic backing sheet released from the underside of the “top sheet” as it was rolled out and torched to the “base sheet”. Occasionally pieces of this plastic backing sheet would remain on the underside of the base top sheet affecting the quality of the weld between the base and top sheets. Water vapour often had the opportunity to build up between the two plies, swelling, blistering and eventually delaminating the sheets.
Can these blisters be repaired? The good news is yes. And it is not as difficult and, therefore, not as costly as repair of blisters on the old tar and gravel roofing. However, to avoid a costly roof replacement don’t let these blisters go unrepaired. I recommend that you contact a reputable roofing company that specializes in “flat roofing” for an estimate and a time frame to conduct the repairs.
Metal roofing in BC limited by pitch
There’s a good reason for this. When rain or snowmelt water rolls off a low pitch roof it travels relatively slowly along the roofing material. The metal sheets overlap each other by only one corrugation at the seam between each sheet. The slow moving water can wick up under these seams and leak through into your attic space. So a 4 in 12-roof pitch is considered the minimum slope that will keep the snowmelt and rainwater moving fast enough to avoid possible leaks.
As well, metal roofing over living areas should have 15 pound breather paper installed between the metal roofing and the strapping or roof sheathing. This breather paper ensures that if condensation builds up on the underside of the metal roofing (from moist heated house air), it will not drip on to your attic insulation. Good attic ventilation will also decrease the possibility of condensation on the underside of the metal roofing. If you really don’t want to change the slope of your roof, consider installing torch-on roofing, tar & gravel or “low slope application” asphalt shingles. These materials are all reliable for low slope roofs.