Do you need felt under roof tiles?
What Does Roofing Felt Do & What Are The Benefits
Well, the original purpose for using roofing felt was to be a temporary waterproof roof whilst homeowners would have to build their own roofs. This method has been used for over one hundred years. When homeowners would remove the shingles off their roof on a weekend, the roofing felt would serve as a waterproof cover. This would temporarily protect their home from water damage over the following week so that the next weekend they could put the new shingles up.
What does roofing felt do
While people are debating on whether roofing felt – otherwise known are tar paper – is still necessary, here are a few reasons why it is still useful. While roofers workers are up fixing the shingles to the roof, the roofing felt creates a safer layer for them to work on, helping to make it less likely that they could slip. By covering your home with roofing felt, your home is temporarily protected from the weather depending on how long it takes to build the roof, creating a waterproof barrier between you and any rain that could potentially come. Another handy advantage is that the roofing felt does temporarily dry once the roof is up and complete.
Assessing the performance of a roof
It is important that a holistic approach is adopted for the performance of a building to be understood, as the roof and walls cannot be taken in isolation: they are an integral part of the building and have an active and continuing relationship with the rest of the building, its environment and its occupants.
The two most commonly encountered ways in which the performance of the roof of an old building has been dramatically and detrimentally altered are by the introduction of insulation and impervious roofing felt.
Typical effects of introducing insulation and impervious roofing felt
- The introduction of insulation over a ceiling creates a ‘cold roof’ (see diagram, below).
- Roofing felt significantly reduces the air movement in the roof space.
- Moist air from the accommodation readily finds its way into the roof space through the ceiling and holes in ill-fitting hatches.
- The amount of evaporation that can take place within the roof is considerably reduced by the introduction of the roofing felt.
- Increased amounts of dampness and moist air are now present within the roof space.
- The timbers in the roof space are therefore increasingly subjected to the conditions conducive for active fungal decay and wood boring insect infestation.
- Any drop in the air temperature provides the atmospheric conditions for the condensation of the moist air to take place.
- The impervious roofing felt provides a high level of resistance to the passage of water vapour and a cold contact surface upon which warm moist air can condense. In these circumstances the rafters in contact with the felt may remain damp most of the time, causing the surface of the rafter to become stained and, in the worst case, rotten.
TYPICAL INSULATION DEFECTS
- Insulation laid so that it covers the eaves, significantly reduces ventilation to the roof.
- Insulation is often laid in contact with the roofing felt. Where the felt is impervious any contact condensation will run down the felt and make the insulation damp.
- Many modern insulation quilts such as fibreglass, in comparison with alternatives that are now readily available, retain moisture. Where an impervious roofing felt has been used, this type of insulation may not dry out readily. In the worst case the insulation becomes a soggy mass at the bottom, causing the feet of the rafters and the ends of the joists to decay.
This brief overview of some of the problems that can be encountered where the roof of an old building has been provided with a secondary barrier and insulation, illustrates that there is a need to evaluate the influence that any changes in the traditional ‘breathing’ performance of the roofs of old buildings is having.
Why use roofing felt paper?
Roofing experts have discovered that adding a layer of protection between your structural roof decking (the layer of wood that covers your rafters) and your roof shingles helps create a better-looking and longer-lasting roof. In fact, there are a number of important ways roofing felt not only protects your roof, but also your residence. For example:
- It repels water
Wind-driven rain or snow can trap water under your shingles, putting your roof deck and inner residence at risk of moisture damage, leaks, rot and mold. Roofing felt helps ensure the water drains off the roof – and doesn’t leak into your home.
- It provides backup protection in the event of ice or water damage
In northern climates, ice or snow dams are another common cause of residential water damage. When the heat from your home melts snow or ice on your roof, the water can then seep into your roof’s nooks and crannies and ultimately into your residence, causing damage to ceilings, walls, or insulation. Your best protection against an ice dam is an ice and water protection membrane which can seal around the shanks of the roof fasteners for a leak-resistant fit. However, roofing felt offers additional protection against leakage, providing an extra layer of water resistance.
- It provides extra weather protection
Although your shingles are your roof’s first line of defense against the elements, having a backup layer of weather protection underneath helps extend the life of your roof deck. And, in the event of a major weather event that breaks your shingles loose, the roofing felt guards your wood deck against rain and water until the shingles can be replaced.
- Roofing felt may be necessary for use with your shingles to meet a Class A fire rating
When shingles are evaluated for their fire ratings, it is done on a small test deck with the roofing felt underlayment in place – without this underlayment, the shingles alone may not meet the Class A fire requirements. Be sure to choose felt underlayments that are approved and compatible with the overlying shingles and therefore comply with building codes. Look for industry standard compliances such as ASTM International or Canadian Standards Association (CSA) references on the product label.
- It protects your roof deck while you work on it
Roofing felt prevents the deck from being exposed to the elements before, or while, the shingles are being applied.
- It improves look and uniformity
Because your roof deck might not lie perfectly straight or flat, a layer of roof paper gives an even, uniform surface upon which you can install your shingles. It can help prevent the “picture framing” effect, or the pattern of your wood decking telegraphing through your shingles, by providing an extra layer on top of uneven wood.
- It prevents wood resin stains
When you use certain types of wood to construct your deck, there is sometimes a risk the wood will leach small amounts of resin over time as it ages. Having a layer of roof felt will block the resin, preventing it from staining or compromising your roof shingles.
ROOF FELT AS A MOISTURE BARRIER
A great benefit to roofing felt is that it can also act as a moisture barrier. When the hot air is rising through the house and reaches the roof, any moisture in the air that condenses on the underside of the shingles, will get caught by the roofing felt. This helps to prevent any damage being done to the wood decking in the long run. The moisture barrier in a roof is highly important nowadays since the way houses are now built with certain extras such as double glazing making air circulation more of a problem. We spend so much time in our homes and throughout cooking, bathing along with all of the occupants in the house breathing, a lot of water moisture gets built up and needs to find a way out. This brings us to the question of the types of roofing felt that we should use.
Is felt waterproof?
The answer is Yes felt is waterproof, the sarking felt which is laid over support rafters or counter battens, beneath the tile or slate battens provides waterproofing. The main purpose of sarking felt is to provide waterproofing to the felt, this stops damage internally creating a barrier and stopping cracked/broken tiles it also helps as an insulation factor for the building.
