I think what those contractors meant to say is that, they never use Ice and Water Shield all over the roof and that they never use starter strip where eavestroughs are installed. The fact of the matter is that they are sticking with the very minimal standard of the Building Code – and it is a minimum standard.
Starter strip or drip edge is especially important at the eavestrough areas because some protection is offered to the edge of the wood sheathing under the shingles by the drip edge, particularly when the eavestrough fills completely and the edge of the sheathing is virtually immersed in water. The drip edge sheds water away from wood sheathing which will rot if not protected – over hanging the shingle an inch or so is not enough – the bottom edge of the sheathing is open under the shingle. Further the edge of the shingle is not a true drip edge – there is enough surface tension that water is able to migrate up the underside of the shingles and make contact with exposed sheathing.
Eave protection is required by Code. The best eave protection is a self-adhering membrane, which because it is adhered to the sheathing provides a positive protection from water exposure. The self-adhered membrane will not rot and provides gasketing around the nails. Felt is loose laid and will rot and provides no gasketing. Felt is loose laid and water is able to migrate under the felt. Building wrap is not acceptable.
The application of a self-adhering membrane (Ice and Water Shield or equal) over the entire roof provides a redundant membrane in the event that a shingle(s) is lost due to wind or other causes – without the membrane there is only bare wood and leaks. The installation of the self-adhering membrane over the entire roof also provides protection against leakage due to ice damming and large build-ups of water due to plugged eavestroughs. Who’s to say that one width of membrane is sufficient for all roofs, everywhere to prevent penetration of water above the single width of membrane – what is in the building code is just rule of thumb. I am sure that you want your clients to be positively protected from leaks and all the damage they can cause and not just rely on the minimum standard or the insistence of some contractors to resist change and keep doing the work the way they always have, in spite of the fact that the old way is dubious at best. Habit has no compelling science or reason to me. “Are you feeling lucky” has no weight with me either – your clients and mine deserve peace of mind when it comes to roofing.
I was at a Building Code Commission in July where I pointed out to the commissioners that I cannot design a roof system according to the Building Code because a roof designed to the minimum standard was probably doomed to failure – they of course were aghast – but when I explained that I had to design to a standard that works, rather than to what the Code says – they agreed and approved a roof system that technically did not meet Code, but was vastly superior in performance.
Some of the misinformation about installing self-adhesive membrane over the entire roof comes from the internet – statements like, ‘the roof can’t breathe” or “the sheathing will rot” are typical and in fact, are garbage thinking. Some manufacturers have used the membrane all over as an excuse as to why there shingles failed and other shoddy thinking. The roof system breathes through the deliberately installed venting – not enough venting is a problem in any situation – the membrane has no bearing on poorly vented roofs. The sheathing can’t rot if there is no contact with water. There is in fact no difference between the strip of sheathing along the eaves and the next strip of sheathing directly above the lower strip. There is no difference in the roof system if the lower strip is covered with a self-adhesive membrane and the next strip above is without, except for the stated problems of leakage and ice damming etc..
Reputable roofers do what is in the specification. Reputable and responsible designers provide specifications that will serve their clients well over the long term. Manufacturers would love to see self-adhered membrane over the entire roof because they know the leak reports and problems will be significantly reduced. And similarly with reputable roofers – they want to do what is best for their customers and for themselves. Installing more waterproofing on a roof has never been a problem – the only problem here is a resistance to change. The bad roofers don’t want to install more because they only sell on price – and many times I see them with installations that don’t event provide the barest minimum.