Should sunken roof be fixed right away?

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Posted by: from Winnipeg
7/13/2019 at 2:50:13 PM


Hoping for expert advice and help on this forum.

I got Shingles installed 2 weeks back and waiting for troughs, sofitt and fascia to be changed as well in one week. I have been living in this house for 4 years now. As I am not an expert (this is my first house in Canada and always lived in the concrete house from where I immigrated few years back), I never paid attention that the roof is sunken on three sides of the house. Fourth side is also not perfect. It became apparent to me when the Shingles were installed and I started comparing with other houses. I believe it is due the nature of Shingles that it became more apparent (I must say that roof was not different even before but I never paid attention and I thought it is old house so Shingles need to be changed which would rectify everything). As I started digging more about sagging/sunken roof on internet, my fears increased.

Two days back, I emailed my roofer about the issues that roof appears to be sunken. Was it due to damaged wood deck which was not changed? (I was not home when Shingles were installed). He came for inspection and told me this is all due to rafter issues and nothing wrong with wood deck and shingles. My concern and I asked him that why they did not disclose this to me before.

He said as he thought it is unnecessary and not required. If it was his home, he would not worry. We also got on to the roof and saw it from above which did not seem too severe as from below. He claimed from below it seems more severe due to illusion and architectural shingles. He also said if I want he can fix rafters as well for approx $250 per rafter (although that was an informal quote). He was not sure how many rafters would be there in total.

I really am not left with any money as already spending more than $8000 on Shingles/troughs, soffit and fascia.

This roofing company is in business for more than 25 years so I am inclined to trust him but fears about safety and further damage are giving me sleepless nights. Could you please guide me what should be my next plan of action. Can I wait and not worry about this. And if in future, I need to sell my house, get the problem fixed then. He gave me advice without going into the attic. Is this possible? Now if rafters are fixed, would that damage the Shingles and troughs? although he said no it will not damage the Shingles and troughs?

How many rafters could there be in a 1200 sq. ft. house? Can you tell me approx cost of fixing this? I understand some of this cannot be answered without looking at the problem but will really appreciate all your help, if I can obtain an idea if this is normal or not. I had obtained 4 other quotes and none of them brought this to my attention. Is it right and normal practice that contractors would not reveal any related issues when any work is being done?

Please advise. Thanks so much.

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Date/Time7/13/2019 at 11:15:12 PM

Dear Anahat,

Before I can provide an informed opinion on your issue it would be helpful to have the following information:

1. The year the house was built?

2. Is the roof deck material plywood sheathing or dimensional board material [3/4" wood]?

3. What is the spacing between the roof trusses [you will need to go into your attic and measure with a measuring tape]?

What I have observed on some occasions is that if your roof deck is plywood sheathing and the truss spacing is 24" on center; it is possible that when the shingles were removed and the plywood sheathing was exposed to direct sunlight and the shingles and nails which held the roof deck in stasis were also removed, warping of the plywood occurred.

This would not be something that anyone can observe beforehand, since it only takes place the day of the installation.

This condition is usually more pronounced and the potential much greater to occur in roofs which do not have sufficient ventilation [which is most roofs in Canada. Building code calls for 1:300 of the attic area to be allocated for ventilation. Half of this area [1:600] should be at your soffit to allow air intake and the other half [1:600] should be near the peak of the various roof areas if your attic space is divided into separate sections to allow for the discharge of air]. When there is a lack of adequate ventilation there is a buildup of moisture in the attic during winter and condensation forms which in turn causes the roof sheathing to absorb more moisture and also damages insulation thereby perpetuating the viscous cycle and increasing your heating costs. In Winnipeg this is obviously no small matter.

In the summertime a lack of ventilation causes an excess buildup of heat - creating a virtual oven in your attic cavity and drying your plywood roof sheathing.

It is possible that this is the cause of your problem. My initial guess is that your roof sheathing warped when it was exposed to the sun.

Unfortunately I do not think you will get any cooperation from the contractor as they will be able to rightly claim that the condition was not a pre-existing condition and the root of the problem was not their fault.

Please check the following:

1. Confirm the underlay that was used at the eaves and the rest of the roof surface area.

2. Count the number of vents and ask the roofer what manufacturer and model of roof vent was used and also ask how many vents were there before the new installation. An easy way to confirm this is often Roofing Contractors will simply install the same number of vents they removed. If they do add vents they will typically charge you for the "extra" vents.

If you have a good underlay and sufficient ventilation it is unlikely that these undulations will cause any leaking. [Pictures would be helpful to see the extent of the issue you are referring to].

Shimming the rafters is unlikely to resolve this issue since the roof deck is likely at its highest point at each rafter location. This is only the case if your roof sheathing is plywood. If your roof decking is 3/4" ship-lap board then the conditions could be very different. This is why I asked the questions I did from the onset.

Unfortunately I am not in Winnipeg - but I hope this has provided you with a better understanding of the issue and if you can provide answers to my questions and post some pictures I will respond further.


Richard - Montbrun Roofing - Saskatoon

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Date/Time7/14/2019 at 12:45:17 AM

You say your contractor talked about repairing rafters' as opposed to trusses'. If your home is built in the 60s or earlier you are more likely to have a stick framed roof with rafters, ceiling joists, possibly a center bearing wall for the ceiling and roof system, and possibly collar ties' to strengthen the rafters and prevent them from sagging.

Not sure if this is the sagging you're referring to; hard to tell without photos or more description. It could be collar ties loosening over the years. It's possible that the rafters could be straightened out to a degree but it wouldn't be very simple, and something not normally done by a roofer who would be only expecting to replace rotted or damaged roof sheathing at the most. You may also be experiencing sagging related to very thin roof sheathing if it's less than 1/2" plywood.

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Shannon from ACT Home Services in Leduc
Date/Time7/15/2019 at 12:22:12 PM

If your home is an older home then this is a common issue. Houses built up to the 1960s often did not have the rafters engineered like they are today. So 50 or 70 years later the rafters have sagged over time. Rot issues are usually localized to small areas so it's doubtful rot is a concern in this situation.

The roofers did not cause the sag and the reason none of the other roofers raised any concerns is because it is fairly common and most home owners are aware of it.

It wouldn't hurt to have the rafters looked at by a framer to make sure they will be ok over the long term.

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