Guide to repair and waterproofing of Jack Arch Concrete Roof

Jack Arch Roof

Jack arch Roof construction can be done in brick or concrete. The arch of the Jack arch roof is either made of brick or of concrete. The arch is supported on the lower flange of mild steel joists (RSJs).  The rolled steel joists are supported at their ends on the walls or on the longitudinal girders. They are spaced at a distance of 1m to 1.5m centre to centre.

Jack arch Roof - Detailed Section
Jack arch Roof - Detailed Section

The rise of the arch is kept equal to 1/12th of the span. Layer of concrete is then poured over the roof to straighten the roof. The  concrete layer thickness over the crown of the arch is not less than 15cm.

Due to the super-imposed load on the arch, tension develops at the ends of the arch. Steel tie rods are placed at the ends of an arch with a suitable spacing of 1.8m to 2.4m.

In this article, we are going to study the causes for leakages in a Jack Arch Roof and remedy to solve the problem of leakage.

The two main causes of Jack-arch roof leakage are:

  1. Poor quality of cement
  2. Inappropriate grade of sand

Repair of the roof

The Jack Arch roof leakage problem has to be fixed and should be so done so as to avoid future recurring water leakage problem. This can be achieved by waterproofing the roof.

Here are the four simple steps to repairing and waterproofing the Jack Arch Roof:

Step one:

The old cement mortar and tiles are to be removed so that the new cement mortar settles and becomes firm over the rough roof surface.

Step two:

After scraping of the cement mortar, fresh cement mortar is laid and left to dry.

Step three:

After the drying of cement mortar, waterproofing is done to avoid any kind of further leakage. Waterproofing material is mixed in a drum of water and splashed over the cement mortar layer. We must make sure that every corner of the roof is to be covered with this waterproofing material.

Step four:

After the process of waterproofing, tiling is done with the help of a suitable adhesive.

6 thoughts on “Guide to repair and waterproofing of Jack Arch Concrete Roof”

  1. Jack arch roofs are not only stronger, they also provide beautiful look to the building. One should take proper precaution while building this type of roof, and keep a correct proportions of cement, sand and water, otherwise, it will effect the durability of roof.


    • Correct Proportions of cement, sand and water applies for every type of roof. Jack arch roof was previously used to cover large spans and was commonly seen in Ancient Palaces. They don’t really make any difference to the exterior of the structure but could make a difference to the interiors.

  2. I used to have patches on my roof since my house is 10 years old,
    after I’ve had it waterproofed, the leaks stopped and It’s like having a brand new roof installed but less expensive.
    I’m so glad I availed of this service.

  3. Few month(Aug, 2011) back we built a residential building, Now the roof is cracking and rain water is leaking inside the house.. Is it a construction problem ? Now what measure should be taken.


    • Hello Pravas,
      The intensity of cracks will determine whether the problem is with the faulty structural design and poor quality construction.
      You should immediately consult a local Architect or a Civil Engineer to take a survey of your house and see what they say.

      Firstly, if it is not structural problem, they might suggest waterproofing your roof to avoid leakage.
      Secondly, if the cracks are deep then there might be a need to lay a layer of concrete on the slab and then waterproof it. This will strengthen the slab as well as prevent leakage during rains.

      Let me know if there is anything more you want to know. After you consult your engineer or an architect, let us know what they suggested.

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