cost to repair sagging roof

What Is The Repair Cost of Roof Sag?

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What Is The Repair Cost of Roof Sag?

Roof sag is something no homeowner wants to see because it can indicate a serious structural problem with the roof deck. A sagging roof repair can cost anywhere from $800 to $2,500 to replace one roof square of decking and shingles, minor roof sag can generate cheaper repairs.

If you're looking for a more accurate average cost to replace your roof sag? The best thing to do is speak to local roofers in your state or area and compare quotes. Fill out the form below and we'll put you in contact with shingle roof experts in your local area. Time to complete: 30 seconds.

Table of costs of a sag roof repair

Here are some roof sag repair costs in more detail based on a range of different roof types and roofing materials.

Fault Average Cost
Replace small sections of roof decking and shingles $250 - $800
Remove pests $250 - $800
Install rafter ties $250 - $800
Replace sections or roof deck and shingles up to 100 square feet  

$800 - $2.500

Install additional rafter support $800 - $2,500
Replace rotten rafters $3,000 - $8,000
Add a new structural ridge beam or rafter ties $3,000 - $8,000


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What causes a sagging roof?

Rain and snow can quickly damage a vulnerable roof such as:-

  •         A roof that is poorly designed
  •         A roof with the wrong choice of roofing materials
  •         A roof in poor condition

Other causes of roof sag include:-

  •         Termites in the roof deck, sheathing or rafters which weaken the supports over time
  •         Incorrect installation so the wrong sized rafters or beams
  •         Ductwork issues which can be caused by contractors removing too much of the frame when installing ductwork

The roof needs to be correctly designed with the appropriate roofing materials and in good condition so that water can run off it to the rainwater goods below. A good design will include metal flashing. If the water can sit or pond or find its way in at any point then it will eventually cause damage to the underlying structure leading to roof sag. A guttering system in poor repair or one that is inadequate for the volume of water can also cause problems even if the roof is performing well.

Poor ventilation in the attic or roof void will exacerbate water problems. It is essential to have enough airflow in the attic otherwise moisture will build up on the underside of the roof making it easier for water to penetrate the roof’s surface. Lack of ventilation will also allow the build up of heat in the summer months which will speed up the deterioration of the roof shingles ageing them more quickly.

Each roof is designed to support a maximum amount of weight, if it has to support more especially for long periods of time then this can cause roof sag. One of the most common problems is excess lying snow which is incredibly heavy and a problem for homeowners in certain parts of the US. But design flaws can also cause weight-related sagging and these include undersized rafters, insufficient sheathing or too few rafter or collar ties – these mean that the roof cannot bear the weight of the roofing material.

Snow removal should only be undertaken by a professional; obviously working at height in very cold conditions is particularly hazardous without the right equipment but incorrect snow removal can seriously damage the roof and will potentially make any roof sagging worse.

How to deal with roof sag

You should contact a roofing contractor for an inspection and report to try and determine the cause of the roof sagging. Most roofing contractors will charge an inspection fee of between $150 and $300. If the roof sag is serious then you may need to consult a structural engineer the costs for which will be in the region of several hundred dollars up to around $1,000.

If water damage is causing the roof sag and this is the most common cause, then the leak needs to be found and repaired. This could mean replacing roof shingles and flashing, repairing the gutters or improving ventilation in the attic. Timbers which are rotten in the roof deck will need repair or replacement; the final cost can only be determined once the extent of the damage has been revealed.

Once the deterioration has been stopped, the actual sag on the roof can be corrected by using angled braces to help shore up the rafters.

What other reasons cause a roof to sag?

In more unusual cases, a roof can sag because the foundation of the house has shifted or sunk and the walls and roof may have moved with this.

How to prevent a sagging roof

First and foremost, make sure your roof is fit for purpose.

  •         The roof design and pitch should be appropriate for the house and the prevailing weather conditions in your state
  •         Make sure the roof shingles or roofing material are not too heavy for the timber deck as this can cause sagging just by itself – shingles which are too heavy for the frame will cause sagging even in a well-constructed roof
  •         Metal flashing should be installed in all appropriate locations such as valleys and joints with chimneys and other roof features like skylights and dormers
  •         Avoid roof overlays which is the installation of two or even three roofs on top of the original deck, this is often done to save money but can cause lots of problems in addition to roof sagging
  •         Keep the roof in good order with annual roof inspections which can highlight small repairs and faults before they turn into something more serious. A roof inspection every year is the only way to be certain of the condition of the roof – not all issues are visible from street level
  •         Keep your roof clear of snow - use a roof rake to deal with lighter snowfall
  •         Keep the attic well insulated and ventilated, this will help prevent the build up of ice dams which can contribute to roof leaks

Once a roof has started to sag, it will only get worse becoming more and more expensive to repair. If the repairs are going to involve more than 25% of the total roof area then the usual recommendation is for a full roof replacement. Search for quotes, compare repair options and find out more about roof leak repair costs.

How to find the right roofing contractor to repair a sagging roof

If you don’t have a regular roofer that you use for small repairs and roof inspections, a sagging roof is definitely your cue to find one and quick.

Ask friends, neighbours or family members if they can recommend anyone. Look around on social media platforms for your area or community and ask for a recommendation. There are also online trader platforms you can use, just key in the type of roofing work you want done and then contractors in your area will get in touch and come and estimate for you. Obtain two or three estimates so you can compare costs.

Questions to ask your roofer

The cost of roof sag repair can be significant so here are some useful questions to ask roofing contractors if you are looking at different estimates:-

  •         Are they certain about the cause of the roof sag?
  •         Is the quote fully inclusive or do they expect to find more problems when they strip off the old roofing material?
  •         What steps need to be taken to prevent the problem from occurring again? If it is a water leak then the answer is obvious but it could be something more complex, such as an inadequate roof frame or roof shingles which are too heavy for the deck
  •         Do they offer any guarantees for the workmanship?
  •         What warranties are offered by the manufacturers for different items like roof shingles, deck and flashing?
  •         Would he recommend a complete roof replacement bearing in mind the extent of the damage and/or the cost?

Getting help with the cost of roof sag repairs

There are grants available at both federal and local level for roofs which are in a poor state of repair and are not watertight. There are also grants available for complete roof replacement if it come to that.

Ask your roofer for details on grants, many roofers are quite au fait with what is on offer as anything that helps towards the cost of a roof repair or renewal could help make their quote seem more palatable and get a signature on the dotted line.

Roof grants tend to aim at two different types of thing:-

  •         Low-income families who are struggling to keep their house dry and weatherproof, this also includes those aged over 60+
  •         Green roofs so grants aimed at encouraging homeowners to consider eco-friendly and sustainable options, this could be a fully fledged green roof i.e. one made of vegetation or just sustainable roofing material choices so shingles which offer good insulation, great for the planet and your energy bills

Roof grants can change quite rapidly so if there is a long time between your roof inspection and the work or you need to consult a structural engineer then make sure the grant is still available or you understand the limitations of any deadline as it might not suit your project.

Some grants are repair only and many have terms and conditions attached which can include a requirement to repay the money if the property is sold within a defined timeframe.


Frequently Asked Questions

Should I have a full roof replacement if my roof is sagging?

This is a matter of debate and discussion with your roofing contractor as it will depend upon the cause of the sagging and how extensive any damage is. The most common cause is water penetration and so this will need to be repaired and it could involve replacing rotten timbers. Once the cost hits around $3,000 for an average roof on a two-storey house or the repairs are going to involve more than 25% of the total roof area, then it could be time to start to think about a whole roof replacement.

What is an ice dam?

An ice dam is a ridge of compacted snow which forms on the edge of a roof and becomes hard preventing melting snow from draining off the roof. The water that backs up behind the dam can leak into the roof causing rot to roof timbers and rafters plus it can also make its way into the house itself causing damage to walls, ceilings and insulation.

How much roof sag is acceptable?

The answer to this is, very little because any roof sag is a cause for concern and could get worse over time.

Can I claim for the cost of repairing roof sag under a home insurance policy?

If the roof sag is essentially caused by a poor maintenance issue then no but if the roof sag has been triggered by damage caused by say a severe weather event then the cost may be covered under your policy.

Is roof sag preventable?

If the roof is correctly constructed with roofing material of the correct weight and the materials chosen are appropriate for the weather conditions, all you have to do is maintain the roof on an annual basis and there should be no real likelihood that the roof will sag. Well-maintained roofs don’t tend to suffer from sag as water leaks and other structural problems are dealt with promptly. No-one wants to get to the point of roof sag as this means there is a significant and expensive problem to resolve.

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