Case study: Waterproofing of a house

Greetings to the Architecture+Design Community.

Introduction

Today I will tell you about an inspection I made to a house, specifically because of roof leaks.

To begin with, I must emphasize that homes need corrective maintenance, but very important also its preventive maintenance, which will extend its life, and avoid further expenses and bad times.

Roof waterproofing has its useful life. In Venezuela it is very common to use a material called "asphalt mantle"; however I have seen in the market waterproofing paints that stand out for their effectiveness and easy application. However, most people choose "the traditional".

Waterproofing with asphalt membranes have a useful life of 5 years; however, in practice, with the conservation of certain conditions and preventive maintenance, this period can be extended.

The following case shows a one-story house with a construction system of structural walls with a solid roof slab and a roof that can be visited. The owner indicates that there are dampness in the house.

The first thing to do is to interview the owner:

1. Is the roof waterproofed?
2. What type of waterproofing was used?
3. Who did it?. Anyone qualified?
4. When was it done?

These questions are interesting to ask. Notice that the man answered me the following:

• The waterproofing of the original house dates back 14 years and has never been re-waterproofed or repaired.

• Eleven years ago he made a lateral enlargement of the house (where the kitchen is now), contracting the complete work to the same construction company that did the original house.

• Six years ago the roof slab was extended on both the main and rear facades, but no waterproofing has been done.

Inspection and symptomatology of failures

Subsequently, I carried out an inspection inside the building to verify the existence of leaks, fissures, cracks or any other anomaly. In fact, I found leaks both in the kitchen and in the main room.

The master bedroom is in the original part of the house, while the kitchen is in the side extension. I was able to verify leaks in a large part of the kitchen, including in areas that underlie the construction joint of the original house with the side extension.

On the other hand, in the exterior areas I also identified leaks, specifically where the front and rear roof slab was extended.

With the above information, I went up to the roof to look for the causes of the problem, and I observed the following:

• The asphalt mantle in the lateral expansion area (16 m2) is in poor condition, it is buckled and cracked over its entire surface.

• The asphalt mantle of the original area of the house (49 m2) is in fair to poor condition. The surface is burnt, cracked and aged throughout, with few bumps. It is noted that it was well adhered at the time.

• It was observed that the neighbor to the north is attached to the house, not fully channeling its rainwater, which increases the amount of water affecting the roof of the inspected house. This neighbor lifted the original mantle at the edge when he built his construction (higher) and made what is called a "media caña", (triangular section filling where the two surfaces intersect), above the asphalt mantle, having been correct to cut an internal strip of the asphalt mantle to erect his construction, then build the media caña and finally overlap a strip of mantle with the original one.

• It was observed that the builder made the mistake of constructing the slope of the lateral extension towards the north boundary, not foreseeing that in the future, this neighbor, who was on a higher terrace, would also extend laterally, causing water stagnation in the inspected house.

• The front slab extension has a steep slope and the rear slab extension was built with a minimal slope, in harmony with the architecture of the house; however, these areas are not waterproofed.

Conclusions

• The waterproofing of the lateral extension was executed with poor quality, even though it was done by a construction company. The membrane was not well adhered at the time.

• The asphalt mantle of the original house is in better condition, even though it is older.

• The main room is affected by leaks, due to the aging of the asphalt mantle of the original area of the house; this has already fulfilled its useful life.

• The kitchen is affected by leaks, due to the progressive deterioration of the waterproofing in the lateral extension of the house, due to water stagnation because of the poorly designed slope, and because of the bad work done in the transition area with the neighbor's house on the north side.

• The leaks in the front and rear roof slab, are due to the absence of waterproofing system.

Recommendations:

• Demolition of the current waterproofing system.

• Modify the slope of the lateral extension of the house towards the rear.

• Installation of the new integral waterproofing system in the entire roofed area, including the junction with the attached house to the north boundary.

• Laying clay tiles on the steeply pitched front roof slab extension.

• Request the neighbor to the north boundary to channel its rainwater correctly (without affecting third parties).

I'm Darwin Perez. Civil Engineer and
Builder of a better world!

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Translated with www.DeepL.com