Roofing Over A Existing Roof Covering

Are you serious or are you insane?

I hear it all the time after inspecting a home where new roofing material has been installed by the homeowner, (or worse, by a roofing contractor) and has been applied to the surface of the old roofing material, why? Why would anyone cover up old, deteriorated, damaged, roof covering material after spending all that time and money? Worse yet, what are the current conditions of the underlayment and plywood sheathing that has been covered up?

The only reason one replaces the roof covering material is that the life expectancy of the roofing material has diminished and expired its intended use and that water and snowmelt is penetrating underside of the roofing material and seeping into areas of the attic or vaulted ceiling or worse, into the interior living spaces of the home. 

If your roof is leaky or not, you may have structural damage from water that may have seeped underside of the roofing material. Adding a new layer over this will seal in the problem and may make the situation worse. Not only that, by adding a second layer or more of roofing material over top, you are adding additional undetermined loads to the roofs structure of the trusses which where only designed and constructed for loads with one layer of roofing material as intended.

As a previous professional building contractor, I have been witness to what happens when a second or more layer of roofing material is applied to the existing roof material. For instance, many years ago, a client of mine contacted me in complaining that his new roof was leaking and there was a very slight sag at one side of the roof approximately half way up the surface of the roof. He informed me that a roofing company overlayed the new metal roofing material over top of the older asphalt shingles. He, the homeowner, questioned this method to the roofer if this method is a normal practice to install the new metal roofing material over top of the old and would there be any future problems in which the roofer informed him that there would not and that it is a normal standard of practice in the roofing industry to do as such.

Well, after hearing this from the homeowner, I informed him that is one of the worst things that can be done in roof covering replacement. I asked the homeowner, what assurance did he get from the roofer that the underlayment, plywood sheathing and flashings where in good conditions and that there was no wood rot deterioration and damage of materials. Further, was there any indications of past or present water seepage into the attic and did he inspect the conditions of the top sections of the trusses for any damaged or deteriorated wood members?

The answer from the homeowner was obvious with a resounding no!

After further discussions with the homeowner and informing him that there is likely damage and deterioration covered up of the plywood sheathing membrane and deterioration of the underlayment and will only be known once both layers of the roofing material is removed, I was given the go ahead to further investigate what has been covered up.

Once the metal roofing material and old asphalt shingles where removed, the underlayment was discovered to be damp at several locations along with various degree’s of deterioration and damage and was not effective at all as a line of defense for preventing water from penetrating to the underside of the underlayment to the surface of the plywood sheathing.

Once the underlayment was removed from the surface of the plywood sheathing and all metal and rubber flashing materials, the plywood sheathing at various locations was damp and wet along with various areas exhibiting various degrees of wood rot and some areas of mold growth development. Worse areas of the plywood sheathing where around the skylights, plumbing air vents, bathroom vent covers, chimney and roof air vents, all having extreme wood rot and where the most likely areas of water seepage entry into the attic. Once the plywood sheathing was removed, the top of the truss cords where stained at various locations even with some exhibiting wood rot.

Before extensive repairs where undertaken, I showed the homeowner what was hidden from view and literate on my statement that new roofing material applied over top of old roofing material is the worse thing one can do to their roof before stripping the old roofing material to the plywood sheathing before reroofing is performed.

On a note, the homeowner contacted the roofing company to see what had been uncovered but insisted that there was nothing wrong in what he did and what has been presently been found had must of occurred within a few short years. When the homeowner told me that, I laughed as this was a long-term issue and that is why he was installing the metal roofing material on top of the old in the first place because your roof was leaking. So if it was, would one not think what the present conditions of the underlayment and plywood sheathing would be if water were seeping underneath and into the attic? What a lame excuse by the roofer!

Anyway, needless to say, because water was seeping into the attic onto the top of the insulation, a good portion of the insulation within the attic had to be replaced. Several of the truss’s top cords had to be replaced and treated with an anti-fungal product to prevent mold growth. New plywood sheathing was added with H-clips which where not installed between the plywood sheathing ends and underlayment was laid on the entire surface of the roof fully fastened and all seams sealed. In addition, all new flashings was installed where needed and as an extra cautionary measure that represents a better building practice and is not required by building code, metal flashing was installed along the entire edge of the roof to protect the exposed ends of the plywood sheathing. Further to this, flashing caps where installed along both sides of the roof gable ends to prevent wind driven rain and snow from entering underside the shingles. With only one layer of roofing material installed, we removed the extra weight from the roofs trusses which they where originally designed and constructed as intended for one layer. As a extra note to this, a few of the top cords where warped and had slight breaks which where later identified to have been caused by the extra loads of the second layer of roofing material and by recommendation of a professional engineer I obtained to inspect all of the trusses, I had to reinforce several of the top truss cords to his requirements.

After all was said and done, the homeowner could not believe how the roof looked which was very different from what the previous roofing contractor did. He indicated that the workmanship and attention to detail was impressive and that the little extras that go beyond the normal roofing standards and practice would protect an expensive investment and prevent any water seepage problems. Further, I gave the homeowner a warranty and guarantee of materials and workmanship as long as a regular maintenance schedule was adhered twice yearly. Yes, you heard me right. Just because a new roof covering and other related roofing components have been installed newly does not mean that regular maintenance and upkeep does not have to be included on a yearly basis, that’s part of homeownership which is the sole responsibility of the homeowner. I gave the homeowner a schedule and that as long the maintenance was performed, I can backup my guarantee of workmanship.

In conclusion, I have seen it all with every roof I had to redo that had been layered over by one or more roof coverings. It has always been the same, the roofer would say that it is a standard practice and is ok to do so. Well, these roofers never get to see the aftermath of their stupidity and lack of knowledgeable building science and what the consequences will be within a few years as they never ever see what happens several years later when the homeowner notices problems.

As the surest way of knowing, the safest thing to do is to have the roof stripped so that it can be examined for potential structural problems and what the conditions are before resurfacing it and to be sure that you are acquiring a professional roofer that knows what he is doing.

Like I always say to my clients, Do It Right – Make It Right.