Window Renovation Costs: Inner Windows and Frame Covers
Kakeru Koumuten Co., Ltd.!
We cater not only to single-family homes but also to rental properties such as condominiums and apartments.
If you have concerns about your windows, such as “It’s cold by the window in winter,” “There’s severe condensation,” “I can hear outside noise,” or “The sash is heavy and hard to open,” please feel free to consult with us.
From ¥30,000 per window
As Little as 1 Day
Completely free
Window Renovation Costs
This is a standard estimate for installation work, including the interior window unit (resin frame + double glazing), measurement, installation, and adjustment.
This method involves installing an additional window inside the existing window to create a secondary glazing. The work is completed in about 1 hour per window without breaking walls or exterior walls. Costs may vary depending on the window size, type of glass (double glazing, Low-E double glazing, soundproof glass, etc.), and whether a frame extension is needed to accommodate the window frame’s depth.
Secondary Glazing Costs by Size
Designed for small windows in terms of both width and height. Effective for preventing cold drafts and condensation in places like bathrooms, washrooms, and staircases.
Brands / Products
LIXIL “Inplus”
This is the most common size of window found in living spaces, located above waist height. It is popular for addressing condensation, drafts, and noise from the road.
Brands / Products
YKK AP “Madorimo Interior Window Plamad U”
This is a moisture-resistant interior window specifically designed for bathrooms. It helps to alleviate the cold in the bathroom during winter and contributes to preventing heat shock. It is installed to fit the window frame of the unit bath.
Brands / Products
LIXIL “Inplus Bathroom Model”
This is a large window that reaches the floor. Due to its large area, it significantly affects the cold and heat in the living room as well as heating and cooling costs, making it the place where the effects of interior windows are most noticeable.
Brands / Products
LIXIL “Inplus” / YKK AP “Plamad U”
This is a standard estimate for work that includes new sashes, glass, removal and installation of existing glazed sashes, frame covering, and caulking.
This method involves covering the existing window frame with a new window frame and sash. Since it does not require breaking the exterior walls or interior, the window can be replaced in just one day. Costs may vary depending on the window size, type of sash (aluminum resin composite or resin), and whether shutters or storm doors are included.
Frame-Overlay Costs by Size
This is suitable for small windows that are prone to opening and closing issues or wobbling. Since the entire sash is replaced, any problems with locks or movement can be resolved at once.
Brands / Products
LIXIL “Replus”
This is a commonly sized window for living spaces. By completely replacing old aluminum sashes with single-pane glass to double glazing sashes, insulation and ease of opening and closing are greatly improved.
Brands / Products
YKK AP “Madorimo Insulated Window”
This is a large window that reaches the floor. The movement of the heavy sliding door becomes lighter, and the insulation and heat shielding performance of the glass also improves. Products with pet doors or ventilation features are also available.
Brands / Products
LIXIL “Replus”
This is a guideline for replacing old storm panels with roller shutters or exchanging them for sash windows with shutters. It can also simultaneously enhance security and typhoon measures.
Brands / Products
YKK AP “Madorimo Shutter”
※The cost is an estimate “per window.” If multiple windows are installed simultaneously, we will provide a quote for each window.
※If the depth of the existing window frame is insufficient, a frame extension will be required separately for the installation of inner windows.
※The cost may vary depending on the type of glass, such as Low-E double glazing, soundproof glass, or security glass.
※The overlay method may not be applicable if there is significant deterioration or distortion of the existing frame. We will confirm this during the on-site survey.
※In the case of apartments, windows are considered common areas, so the overlay method (sash replacement) may be restricted by management regulations. The installation of inner windows is usually possible within the privately owned area.
※Window insulation renovations may be eligible for subsidies from the national or local government. There are requirements regarding eligible products, performance, and application timing depending on the system, which we will inform you about during the estimate.
If you send us a photo of the entire window, the inner dimensions of the window frame (width, height, depth), and the type of window (sliding, vertical sliding, fixed, etc.), we may be able to provide a rough estimate.
Window insulation renovations may be eligible for subsidies from the national and local governments. The main programs available in our service areas of Tokyo and Kanagawa Prefecture are as follows. National and prefectural programs may be used in combination, and if conditions are met, construction costs can be significantly reduced.
The installation of interior windows, replacement of exterior windows (cover method), and glass replacement are eligible. Applications must be made by registered contractors, and the use of high-performance products registered as eligible is a condition. Applications will close once the budget limit is reached.
Subsidy for Insulation Window Renovation of Existing Homes
This applies to high insulation windows (interior windows, exterior window replacement, glass replacement) of existing homes in the Tokyo area. Windows with security features have an expanded limit. It may be possible to combine this with national subsidies.
Subsidy for Energy Conservation Renovation of Existing Homes
This program requires window insulation renovation. It applies to existing homes in the prefecture, and it may be possible to combine this with national subsidies. There may also be unique programs in your municipality, such as Yokohama City or Kawasaki City.
※The above is an estimate for the fiscal year 2026. The subsidy amount, grant rate, application period, eligible products, and the possibility of combining with other programs are defined for each system and may change depending on the fiscal year and budget situation.
※Even if you combine national and prefectural programs, the total amount of subsidies will not exceed the construction costs.
※Whether you can use the subsidy depends on your region, housing, and construction details. If you are interested, we will provide information during the estimate, so please feel free to consult us.
Secondary Glazing or Frame Overlay?
The existing window remains as is, and an additional window is installed on the interior side. The air layer created between the double windows acts as insulation, significantly reducing cold, condensation, and noise. This method does not require wall demolition and can be completed in about one hour per window, making it a recommended option for those looking to keep costs down and achieve effective results, especially for apartment residents.
A new frame is placed over the existing window frame, and the sash and glass are completely replaced. The window can still be opened and closed as a single unit, and cleaning efforts are not increased. This option is recommended for those who want to resolve issues such as sash distortion, lock malfunctions, or difficulty opening the window, and for homeowners looking to refresh the appearance of their houses.
Which Method Suits You?
- Want to easily improve cold, condensation, and noise → Interior window installation
- Heavy sash, broken lock, or rattling → Cover method
- Living in a condominium → Interior window installation (often cannot be replaced due to regulations)
- Want the highest insulation performance → Combination of cover method + interior window is also possible
Window Renovation Projects
We installed interior windows on a waist-high window that had condensation on the entire glass surface and mold on the window frame during winter. The existing window was left as is, and a resin sash interior window was installed on the indoor side. Condensation has significantly decreased, and the coldness near the window has eased.
We replaced an old aluminum sash that had become heavy to open and close with a new double glazing sash using the cover method. Since the existing frame was left intact and a new frame was placed over it, the work was completed in one day without breaking the walls or exterior walls.
When to Renovate Your Windows
The lifespan of aluminum sashes varies depending on usage conditions and installation environment, but a general guideline is about 20 to 30 years from installation.
However, single-pane glass aluminum sashes have low insulation performance regardless of their age, and it is said that about half of the heat in a home escapes through the windows. Windows that are “not broken but cold or have condensation” can be greatly improved with just the installation of interior windows.
If you notice the following symptoms, please consider installing or replacing interior windows.
- Cold near the window in winter, and the room is slow to warm even with heating
- Condensation on window glass or sashes, leading to mold on curtains or window frames
- Concern about outside noise from cars, trains, or conversations
- Heavy sashes, catching, or locks (crescents) that are hard to engage
- Wind entering through gaps in the sash, or wet window frames on rainy days
- Rubber packing deteriorating, causing the glass to rattle
Parts such as rollers (the rollers under the sash), locks, and rubber seals may reach their replacement period before the sash itself. Depending on the symptoms, improvement may be possible with just part replacement, so we will provide suggestions during the on-site inspection.
If condensation is left untreated, it can lead to mold and corrosion of window frames, wallpaper, and flooring. If you are struggling with condensation every winter, please consider early installation of interior windows.
Get a Window Renovation Quote
If you send us photos and measurements of your windows, we may be able to provide an estimated quote.
Benefits of Secondary Glazing
By installing interior windows, an air layer is created between the existing window and the new window. This air layer blocks outside cold air, heat, and noise, resulting in the following effects:
- Insulation and Energy Saving: Reduces the influx of cold air in winter and hot air in summer, improving the efficiency of heating and cooling.
- Reduction of Condensation: The inner window becomes less cold, helping to prevent condensation and mold growth.
- Soundproofing: Reduces noise from roads and train tracks, as well as sound leakage from inside the room.
- Security: The double window design makes it more time-consuming for intruders to break in, serving as a deterrent against burglary.
- Heat Shock Prevention: Mitigates sudden drops in temperature in bathrooms, toilets, and changing rooms.
Interior windows typically use resin frames, which are less conductive to heat compared to aluminum. The glass can be selected according to purpose, including single-pane glass, double glazing, Low-E double glazing, and soundproof laminated glass.
Before Renovating Your Windows
To install interior windows, a depth of about 7 cm is required on the indoor side of the existing window frame. If there is insufficient depth, a frame extension will be added for installation. Additionally, if there are curtain rails or blinds inside the window frame, relocation may be necessary.
Since the cover method uses the existing window frame as a base, installation may not be possible if there are significant distortions, corrosion, or signs of water leakage in the frame. Also, since a new frame will be placed over the existing one, the glass area (opening) will be a few centimeters smaller than before. We will explain the condition of the frame and how it will look after finishing during the on-site inspection.
Since the window frames in condominiums are considered common areas, permission from the management association is required for the cover method (frame replacement), and there may be cases where it is not permitted. The installation of interior windows is usually possible as part of the private area work, but please check the management regulations and allowable construction times in advance.
Renovate Several Windows Together
If there are two or more windows in one room, installing an interior window on just one will reduce its effectiveness as cold air and noise can still enter from the other window. By performing the work for the entire room or the whole house at once, you can fully experience the benefits, and the construction cost per window can also be reduced. There is also the advantage of more easily meeting the requirements for subsidies (number of windows and area).
Is Secondary Glazing Right for Your Home?
We will check the depth of the window frame, the condition of the existing frame, and the type of window during the on-site inspection.
Secondary Glazing Installation
Interior windows can be installed in about 1 hour per window without breaking walls or exterior walls. On the day of construction, you only need to slightly move furniture and curtains around the window, and you can use it on the same day.
Before installation, the aluminum sash condenses on the entire glass surface in winter, causing the area near the window to become cold.
Measure the width, height, and depth of the existing window frame in millimeters, and check whether a frame extension is necessary and the type of window. Based on the measurements, we will custom order the interior windows to fit perfectly in the window frame.
Fix the upper frame, lower frame, and vertical frame for the interior window to the inside of the existing window frame with screws. Install while checking for horizontal and vertical alignment, and install the frame extension first if necessary.
Insert the glazed sliding sash with glass into the installed frame. Adjust while checking if it opens and closes smoothly and if the lock secures properly.
Make final adjustments to ensure it closes without gaps. Clean around the window, and it will be handed over in a usable state on the same day.
Frame-Overlay Installation
The cover method can be completed in about half a day to a day per window. Since it does not involve breaking the exterior walls or interior, scaffolding and extensive protection are generally unnecessary.
Before the work, the paint on the frame had peeled due to aging, and the old aluminum sash had become heavy to open and close.
We remove the glazed sash, screen, rails, and other parts from the existing sash. The window frame is left as is, and we clean and check the substrate to prepare for the new frame overlay.
We overlay the new window frame over the existing one and securely fasten it with screws. We check for level and vertical alignment, ensuring there are no gaps between the existing frame and the new installation.
We install the new glazed sash and screen, adjusting for smooth opening, closing, and locking. The junctions between the old and new frames are waterproofed with caulking on both the indoor and outdoor sides.
We install decorative covers (trim) around the indoor and outdoor frames to conceal the existing frame and finish neatly. A final check and cleaning are performed, marking the completion of the work.
Service Areas
Based in Aoba-ku, Yokohama, we primarily serve Kanagawa Prefecture and Tokyo. We can also accommodate some areas in Chiba Prefecture and Saitama Prefecture, so please feel free to consult with us.
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Akishima City / Akiruno City / Adachi Ward / Arakawa Ward / Itabashi Ward / Inagi City / Edogawa Ward / Ome City / Ota Ward / Katsushika Ward / Kita Ward / Kiyose City / Kunitachi City / Koto Ward / Koganei City / Kokubunji City / Kodaira City / Komae City / Shinagawa Ward / Shibuya Ward / Shinjuku Ward / Suginami Ward / Sumida Ward / Setagaya Ward / Taito Ward / Tachikawa City / Tama City / Chuo Ward / Chofu City / Chiyoda Ward / Toshima Ward / Nakano Ward / Okutama Town / Nishi-Tokyo City / Nerima Ward / Hachioji City / Hamura City / Higashi-Kurume City / Higashimurayama City / Higashiyamato City / Hino City / Fuchu City / Fussa City / Bunkyo Ward / Machida City / Mitaka City / Minato Ward / Musashimurayama City / Musashino City / Meguro Ward
View service areas in Kanagawa Prefecture
Aikou-gun Aikawa Town / Ashigarakami-gun Oi Town / Ashigarakami-gun Kaisei Town / Ashigarakami-gun Nakai Town / Ashigarakami-gun Matsuda Town / Ashigarakami-gun Yamakita Town / Ashigarashimo-gun Hakone Town / Ashigarashimo-gun Manazuru Town / Ashigarashimo-gun Yugawara Town / Isehara City / Odawara City / Kamakura City / Kawasaki City / Kawasaki City Kawasaki Ward / Kawasaki City Asao Ward / Kawasaki City Saiwai Ward / Kawasaki City Takatsu Ward / Kawasaki City Tama Ward / Kawasaki City Nakahara Ward / Kawasaki City Miyamae Ward / Koza-gun Samukawa Town / Zushi City / Chigasaki City / Nakagun Oiso Town / Nakagun Ninomiya Town / Hadano City / Hiratsuka City / Fujisawa City / Miura-gun Hayama Town / Miura City / Minami-Ashigara City / Yokosuka City / Yokohama City / Yokohama City Aoba Ward / Yokohama City Asahi Ward / Yokohama City Izumi Ward / Yokohama City Isogo Ward / Yokohama City Kanagawa Ward / Yokohama City Kanazawa Ward / Yokohama City Konan Ward / Yokohama City Kohoku Ward / Yokohama City Sakae Ward / Yokohama City Seya Ward / Yokohama City Tsuzuki Ward / Yokohama City Tsurumi Ward / Yokohama City Totsuka Ward / Yokohama City Naka Ward / Yokohama City Nishi Ward / Yokohama City Hodogaya Ward / Yokohama City Midori Ward / Yokohama City Minami Ward / Sagamihara City / Sagamihara City Midori Ward / Sagamihara City Minami Ward / Sagamihara City Chuo Ward / Ebina City / Atsugi City
trust Kakeru Koumuten!
By renewing your windows, you can alleviate winter cold, summer heat, condensation, and noise, which can also lead to savings on heating and cooling costs. We will propose the optimal method after checking the depth of the window frame, the condition of the existing frame, and the regulations of your condominium.
On-site surveys and estimates are free. We welcome inquiries about subsidies and comparative estimates, so please feel free to contact us.
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contact Kakeru Koumuten Co., Ltd.
Kakeru Koumuten is a young company whose team is, on average, in their late twenties, but our skills are second to none.
Our greatest strength is that we handle scaffolding, roofing and painting entirely in-house. In an industry where these tasks are usually divided among contractors, our complete service simplifies project management and helps keep costs down. Above all, if a problem arises, we respond promptly.
We proudly describe ourselves as the youngest and most helpful renovation company in Kanagawa!
