Staff Blogs/News

What is Kasagi? We will explain in detail the role of Kasagi and how to repair it!

Hello! This is Kakeru Construction Co., Ltd.!


Here we will introduce about “Kasagi”

We will also introduce actual implementation examples at Kakeru Construction Co., Ltd.!

・What part is Kasagi?

・I wonder if it’s possible to request repairs only for Kasagi…

・Lately, I’ve been concerned about rain leaking on my balcony…

I often hear people’s concerns and questions.

In this article, I would like to introduce you to Kasagi so that you can clear up those questions!

If you are having trouble with Kasagi, please leave it to Kakeru Construction, which has a wealth of construction experience!

What is Kasagi?


In architectural terms, 『kasagi』 refers to a finishing material that is attached to the top of a horizontal structure such as a balcony, veranda, or parapet. Kasagi is a material or part used for waterproofing.

The material varies depending on where it is installed, and aluminum, galvanized steel, and galvanized steel plates are mainly used outdoors, while wood is often used indoors. This time we will explain about Kasagi used outdoors!

Trivia: People often think that a balcony is a balcony because it is wide and a balcony is a balcony because it is narrow, but the size has nothing to do with it!

The one with a roof is a veranda, and the one without a roof is a balcony!

Kasagi’s role


The main role of Kasagi is waterproofing. Of course, there is also the meaning of installing it to match the exterior design!

It is true that rain leaks from Kasagi are very common.

Kasagi has the role of preventing deterioration of walls and structures from rain, wind, and dust in the air. This is especially important for walls and rooftops that are affected by rain and wind.

The caps on verandas and balconies are made waterproof to prevent rainwater from penetrating inside the waist walls.

Kasagi is surprisingly little known, but you can think of it as a small roof that protects your home.

Points to note regarding Kasagi construction

①joint part






Care must be taken if the joints between the overlapping parts of the Kasagi are cracked or damaged. Rainwater may enter through the cracks.

Joints on verandas and balconies are susceptible to deterioration due to UV rays and temperature differences, so be sure to check for cracks.

②Deterioration of the Kasagi body

The Kasagi itself may deteriorate. If the Kasagi deteriorates, the waterproof function will decrease. Basically, Kasagi deteriorates due to UV rays, rain, etc.

Metal caps are particularly susceptible to rust.

If the Kasagi itself deteriorates, water can get inside, leading to corrosion of the wood of the structure and leaks.

There are many cases where Kasagi sheet metal is rusted and has holes!

③Nail/screw fasteners







Be careful if the Kasagi’s fasteners are fastened with nails or screws from directly above. When it comes to roofs and capstones, it is basically a no-no to drive nails into the sheet metal from directly above.

If you fix the sheet metal with ceiling hammering, rainwater will seep in through the nail holes, greatly increasing the possibility of corrosion of the base and leakage. If you have no choice but to hit the ceiling, be sure to use a primer to seal it!

Even if it is nailed from the side, the nails will become loose as time passes, and if rainwater seeps in through the gaps, the interior will begin to deteriorate.

What is the repair/repair method for Kasagi construction?

Now, we will introduce how to repair and repair Kasagi sheet metal.

caulking repair


If a leak occurs because the caulking has deteriorated, deterioration can be prevented by simply reapplying the caulking.

The main areas where caulking is applied are the joints between the caps, around the handrails, around nails and screws, and where the caps connect to the exterior walls.

If it has cracks, or has become thinner and has gaps at both ends, it’s probably time to re-hammer. Replacement involves removing the existing sealant and filling it with new sealant.

Kasagi exchange

If the corrosion has progressed to the inside of the cap and there is damage caused by rain leaking indoors, it will be necessary to cover or replace the cap.

The construction method for Kasagi varies depending on the material. In the case of galvanized iron or metal, our company basically performs cover construction.

If the material of the cap is aluminum, it cannot be covered and will need to be replaced.

If the inside of the Kasagi is severely corroded or leaking, it will be necessary to replace everything from the foundation. In the case of replacement, the existing materials and foundation must be dismantled. After reinforcing the base, we will apply the veneer and install the new material.

What is Kasagi’s cover construction? ?

Cover construction involves placing field boards and roofing sheets on top of the existing Kasagi and wrapping them with galvanized steel plates.
To prevent corrosion and deterioration, the wood is coated with a water-repellent material before being processed into sheet metal.

Painting the Kasagi part


Kasagi can also be repaired by painting. Even though it is called repair, it only extends the waterproofing effect of the Kasagi itself and maintains its beauty.

Just because you paint it doesn’t mean it will prevent leaks.

Even though it maintains its beauty, painting is not recommended as the paint will peel off over time. On the other hand, in some cases, the appearance may deteriorate after a few years.

If the Kasagi is made of aluminum, it will peel off quickly even if painted, so be careful!

Construction explanation of Kasagi sheet metal replacement

I explained about Kasagi above, but I will explain it in an easy-to-understand manner based on the construction photos! This is the actual results of construction at Sho Construction!

1.Removal of existing Kasagi


We will remove the existing Kasagi! You can see that the base has deteriorated.

2.Kasagi underlayment replacement


Cut the new base to the correct size and secure it with screws!

3.roofing sheet upholstery


We will put a roofing sheet (waterproof sheet) on top of the base.The roofing we used is Tajima Roofing/Tadis Self!
It is made of a material called delayed adhesion modified asphalt roofing and is said to last twice as long as regular asphalt roofing.
If the roofing is solid, it will not leak as it serves as primary waterproofing!
I’ll attach it firmly so it doesn’t fly away.

There is also an article that explains about roofing sheets! Please take a look if you like!

4.Attachment of accessories/arabesque


Before constructing the main body, we will process and construct the arabesque!
The accessories used will be galvalume steel plates!

5.Kasagi installation and caulking in various places


After processing the accessories, we will attach the Kasagi. We will apply caulking to the overlapped parts of the Kasagi and the connection with the outer wall to make it waterproof! If this caulking is not done properly, rainwater will enter through the gaps and cause deterioration to accelerate!

Kasagi construction example


◇Mr. K’s residence in Sagamihara City: Parapet

◇Totsuka Ward, Yokohama City: Veranda

◇Mr. K’s residence in Kohoku Ward: Balcony










For the sheet metal of the Kasagi and gables, galvalume steel plates are processed to match the building!
The sheet metal we often use at our company is JFE Steel Sheet/Kiwami MAX!

The durability is about 35 years, and there is a 25-year puncture guarantee!

In addition to Kasagi, we also provide information on various construction projects as well as useful information for construction!

There are some construction projects that can lead to losses and failures if you are not aware of them! Before you make a mistake or make a loss, acquire as much knowledge about construction as possible so that you can identify a contractor!

Testimonials from customers who have actually completed construction work

■Mr. S, Aoba Ward, Yokohama City

I was concerned about the deterioration of the Kasagi and requested a quote.

The handrails had become brittle and we had them replace them, but they explained everything from pre-construction to post-construction in detail, making it very easy to understand and allowing us to entrust the work to them with peace of mind. thank you very much.

■Mr. A, Miyamae Ward, Kawasaki City

We asked for roof construction and Kasagi construction. We received estimates from three companies, but compared to other companies, Sho Construction’s estimate was detailed, very easy to understand, and the cost was low, so we went with Sho Construction.

I didn’t know much about Kasagi, but he taught me everything one by one, which was very helpful.

Q&A about Kasagi sheet metal construction

Is it possible to do construction only on Kasagi?

Yes, of course it is possible. At our company, we also carry out a lot of construction work that only involves Kasagi.

Do I need scaffolding to do the balcony Kasagi construction?

Basically it’s not necessary. However, if construction is difficult, scaffolding may be installed partially.

What is the average cost of Kasagi construction?

The price varies greatly depending on the material used (aluminum or galvalume copper plate), but basically the average price is 1m/~50,000 yen!

For Kasagi sheet metal work, leave it to Sho Construction!

Kasagi prevents rainwater from entering and protects balconies, balconies, parapets, and other areas of your home. If you notice rust on the cap wood, cracks or damage to the caulking, rot or leaks under the balcony or verandah (eaves), you need to take immediate action.

If you wish to maintain it, we will repair it with caulking or coat it with paint. If the interior has corroded due to rain leaks, it would be a good idea to replace the cap and repair it.

At Kakeru Construction Co., Ltd., estimates and inspections are of course free of charge!

We put our customers first and are confident in our execution! At Kakeru Construction, we do not charge fees until the customer is satisfied with the installation!

After the implementation, there are things that I am even slightly concerned about, and I am still not satisfied with it! If you have any questions, please feel free to contact us and we will respond as soon as possible!

Click here for useful information about exterior renovation!

Consultations on LINE are also welcome◎

We also update our Instagram from time to time ◎ Please follow us ◎


For roofing, guttering, and exterior work and repairs in Kanagawa, contact Kakerukoumuten Co., Ltd..

AAA is a young company with an average age in the early 20s, but our technology is second to none.

One of our greatest strengths is that we can do all of our own scaffolding, roofing, and painting work. In this industry, where work is generally divided, we are able to provide a complete set of services, which saves time and effort in management and reduces costs. Above all, if there is any trouble, we will come to you right away!

We can confidently declare this. We are the youngest and most friendly renovator in Kanagawa!