Blowing from under the sill of a plastic window, what to do: step-by-step instructions

High-quality window structures should work flawlessly after installation. However, many owners begin to experience a draft with the onset of cold weather, blowing from under the windowsill of a plastic window. What to do if a crack appears under the frame causes inconvenience. If double-glazed windows have been installed recently, the warranty period has not expired. If the breakdown was not your fault, then it is reasonable to contact the manufacturer. Employees will fix it for free. If this is not possible, there are several options for independent dismantling, but after finding out the reasons for the blowing.

Blowing from under the windowsill

If it blows between the double-glazed window and the window sill, then the thermometer in the room probably drops sharply and excess heat escapes. The situation threatens significant heat loss and the occurrence of colds in the owners. Significantly shows through even when a gap of 0.5 mm appears. Although, you shouldn't fall into despair.

In order not to return to the problem again after self-remodeling, you need to find out where the blowing is coming from: from the sashes, profile, hinges, joints.

The exact location of the draft is determined by the flame of a lit candle brought to the joint. If it starts to fluctuate, it means there is a draft in that place. Surely the double-glazed window is thin, single-chamber. It is better to replace it, because it is difficult to correct the situation on your own.

Cover with sealant

This method is suitable if the gap between the window sill and the window frame is not very large . In addition, compared to other methods of combating drafts, this is the cheapest.

Defects are eliminated using a transparent sealant. Before using it, the gap should be cleaned of dust and dirt, degreased, and dried.

The gap between the frame and the window sill must be cleaned of dirt

Then, using the tube nozzle, apply the maximum possible amount of the substance until it is completely filled.

For the easiest way to eliminate a defect, use a sealant

To get a beautiful seam, run the edge of a 10-ruble coin along it. Do this in a continuous motion to avoid crooked seams.

The advantage of this method is that all the work takes a matter of minutes. Disadvantage: fragility. After two years, the sealant begins to peel off and darken.


Two main factors are known:

  1. Defective window design.
  2. Broken installation technology.

If a marriage is noticed. If the installers are to blame for making mistakes during installation, it is worth notifying the installer about this during the warranty period. Specialists are required to come and reinstall the structure free of charge.

Even a small gap can be the cause of blowing

If the warranty period has expired, but the double-glazed windows were purchased from a reputable company and defects are excluded, then we can only assume that siphonitis is due to:

  • poor sealing of tides;
  • insufficient number of frame attachment points;
  • poor-quality installation of the structure or interface unit (window sill-window opening-frame);
  • subsidence of the polyurethane foam (destruction of the seam) in the case of using low-quality adhesive and sealant;
  • savings on foam by unscrupulous installers;
  • distortion of the glass unit against the backdrop of shrinkage of the building;
  • wear of the seal;
  • making spacer pads from the wrong material.

Attention! It is important to approach the purchase of plastic products responsibly. Otherwise, under the influence of cold winds, the seal will quickly wear out and the profile will lose strength.

Simple adjustment of plastic windows: the blowing from below is quite strong

It is clear that if it is blowing from below the sash of a plastic window, then most likely the problem is in it, and not in the main structure. There may also be several reasons for this, for example, improper clamping of the sash, as well as damage to the sealing rubber, which you can easily learn how to change. Everything is simple here, you don’t even need to bother, since this problem is solved within twenty minutes.

Photo from the site:

  1. Adjustment of the sash pressure must be carried out from the end of the sash, where there is a special trunnion that will need to be turned in winter mode. Simply grab the part with pliers and turn it until it stops, and the mechanism will rebuild everything else itself.
  2. You can also adjust the fittings as a whole so that they work correctly, ensuring correct, uniform pressure around the entire perimeter.

If it blows in the lower part, but closer to the slope area, then you will have to disassemble them, foam all the joints, and seal the slopes again. If they were plastic or made of sandwich panels, for example, then this will not be difficult at all, the structure just needs to be disassembled and then reassembled; things will be much more difficult with drywall, and even more so with plaster.

How to seal the gap between the window sill and a plastic window

When the causes of blowing are clarified, they are eliminated depending on the nature of the defect. If a technician is called, then while waiting you can temporarily block the flow of cold air by placing any barrier (book, blanket, piece of furniture).

If you decide to seal the gap between the window sill and the plastic structure yourself, then ways to solve the problem:

  1. Closing with profile.
  2. Using sealant.
  3. Reinstallation, insulation of window sill.

Silicone sealant

It blows between the window and the frame, a gap appears with a cold bridge penetrating into the room through it due to the destruction of the mounting seam and poor sealing of the joints. Frost-resistant silicone sealant, which should be used to go through the cracks, will help solve the problem. To work you will need:

  • construction knife;
  • masking tape;
  • gun for applying sealant;
  • the profile section is 2 cm longer than the window frame.


  1. Clean the joint between the frame and the window sill from dirt, dust, and old foam. It is advisable to first remove the low tide from the street side.
  2. Slightly widen the gap with a construction knife.
  3. Cut off the perforated part of the corner. Use a knife to sharpen the cut area.
  4. Make small holes in the slopes where the profiles will be mounted.
  5. Apply tape to the frame to save silicone.
  6. Apply an even layer of sealant from a gun along the entire length of the joint. Fill the inside of the gap to the maximum. Also process the pointed wedge of the profile.
  7. Insert a corner into the hole in the slope and tuck it into the gap. Press down to help the sealant set faster.
  8. Remove the tape. Remove any remaining silicone from the window frame with a cloth soaked in alcohol in case of accidental contact.

Plastic profile insert

Labor-intensive but reliable method. To install a profile yourself:

  1. Mark the length of the window sill. Take a profile that is 2 cm longer.
  2. Using a sharp knife, remove the perforated part, leaving 1 cm to the corner and a 2 mm bend.
  3. Sharpen the edge of the profile so that it fits tightly and easily into the gap between the wall and the window sill.
  4. Make holes in the corners of the walls (width - 1.5 cm). Clean, degrease and dry them.
  5. Fill with a thick layer of sealant. Apply the same glue to the profile.
  6. Insert one end into the hole in the wall. The other sharpened edge is in the gap.
  7. Align the profile along the entire length of the structure. Fix, press with your hands for a few minutes for better fixation of the glue.
  8. Remove any remaining sealant before it dries.

Replacing the seal

The elastic band located on all sides of the glass unit stretches and dries out over time. To prevent it from blowing, you simply need to replace it with a new seal. Then treat with silicone.

Reinstalling the window sill

A last resort when there is really a lot of blowing out the window. Dismantling on your own is carried out carefully so as not to disrupt the integrity of the structure as a whole:

  1. Cut off the old polyurethane foam on the slopes without touching the plastic.
  2. Remove the window sill.
  3. Walk over the work surface with a wet cloth or vacuum cleaner.
  4. Identify defective areas. Fill with foam or sealant.
  5. Apply a layer of sealant to the rib part of the structure. Fix, press to the previous place. Wait until the foam dries completely. Attention! To strengthen the window sill in the correct position, you can place a heavy object. This way the structure will not warp over time.
  6. Plaster the slopes.

The cracks are sealed with transparent sealant with a special nozzle quickly and easily. Although, the method is only suitable when the joints diverge a short distance. In order for the putty to last more than 2 years, you need to pour the maximum amount of it into the gaps. Then it is advisable to go along the seam with the edge of a large coin (10 rubles). This way the sealant will become smooth and beautiful.

If difficulties arise during independent dismantling, then it is better to entrust the entire process to professionals.


If there is a strong blow in the window, it is better to immediately begin global measures, namely, reinstalling the window sill.

How to do it right:

  1. First you need to dismantle the canvas: carefully run a sharp knife under the window sill, cutting off the mounting foam, and cut off the sealant on the slopes. Do not touch the plastic.
  2. Carefully pull out the window sill.
  3. Use a vacuum cleaner to clean the entire work surface. This will reveal all the cracks.
  4. Fill the cracks with sealant or foam. The method with sealant is more reliable, the substance fills defects better.
  5. Apply polyurethane foam to the canvas. Return it to its place and press down for better fixation. It is most convenient to control an even angle using a mounting level.
  6. While the foam dries, it is recommended to strengthen the position of the window sill with heavy objects so that it does not warp.

We recommend: How to remove cracks and squeaks in laminate flooring without disassembling the floor

All that remains is to plaster the slopes. If everything is done correctly, improvements will be noticeable immediately.

Blowing from under the hinges

Even when installing a high-quality plastic structure, the hinges gradually become loose. In winter, cold bridges begin to move away from them. To solve the problem, the area to be dismantled is identified. The hinges are directly adjusted with the Asterisk key after removing the plastic protection from them.

Attention! In areas near the window, it is recommended to tighten the hinges more.

It happens that window fittings are not adjusted correctly. The window sash dangles and does not press tightly against the frame. It is worth opening and closing the double-glazed window one at a time and checking whether it moves smoothly and smoothly. If a draft seeps through the frame, then the transom probably remains in summer mode during the winter. We correct the situation by tightening the trunnions clockwise until they stop, having first opened the doors.

Where does the water on the windowsill come from?

Water appears on the windowsill sooner or later, but not in all houses. If the apartment has central heating, you most likely will not find out about this problem. The fact is that sufficient heating and proper ventilation of the room do not contribute to the appearance of moisture on the windows.

Water on window sills appears due to the fact that moisture condenses on the windows and flows down under the influence of its own gravity. In most cases, this happens at night, when the air temperature drops sharply.

To avoid the appearance of water, it makes sense to take care of ventilation. It's better if it's forced. But there will also be a lot of benefits from natural ventilation if you leave the window ajar at night. This will be enough to prevent the windows from fogging up.

  • Information on which wooden window sills to choose.
  • Do-it-yourself window sill restoration - see information from an expert here
  • Do-it-yourself repair of plastic window sills - see tips from the master here.

Moisture will not appear even if heating radiators are installed under each window. If the house is warm enough, the moisture will not have time to condense and will evaporate.

Also watch an educational video about drafts from plastic windows

Condensation on the glass inside the window. What to do if water leaks from a crack

Often a problem does not come alone. Poorly installed double-glazed windows not only blow, but also seep in moisture after rain. The result is an accumulation of condensation, frost, and icing of the lower parts of the window. The reason is that there is no air circulation in the room and the humidity is high.

Reference! According to GOST 24866-99, the accumulation of condensation on the inside of the glass unit is not a malfunction. If condensation accumulates inside the glass unit, then this is an obvious defect.

First, we find out the causes of condensation and try to eliminate it. If the problem occurs due to high air humidity, it is recommended to ventilate manually by opening the transom. You can use a supply ventilator. Although the efforts will be in vain if the double-glazed window does not match your climate zone.

A single product that does not suit the climate must be replaced. In cold weather it will probably freeze.

Consecutive steps to solve the problem:

  1. Remove the outer slope, because the foam insulation underneath wears away (thinner) if condensation appears.
  2. Remove the old layer of polyurethane foam.
  3. Install support blocks if necessary. Then - vapor barrier tape into the formed groove.
  4. Foam the space under the frame. Cover the sealing layer with insulating tape.

Polyurethane foam is used to fill cracks

Attention! When purchasing a structure, you should find out whether it is suitable for your climate zone. Single-glazed windows are more likely to freeze in winter. It is better to take 2, 3-chamber ones with increased thermal insulation characteristics. To prevent blowing from the transom, it is advisable to monitor the actions of the technician during installation. They should not skimp on polyurethane foam and thermal insulation tape.


One of the preventive measures is to contact a professional company for installing plastic windows. Then the risk of receiving poor-quality installation is greatly reduced.

To prevent air from escaping from the frame, the rubber seal must be cleaned once a year. Accumulated dust and dirt prevents the window from closing tightly.

If the windows are old and it is not yet possible to replace them, then it is recommended to insulate the space under the window sill. To do this, you can use the following materials: polystyrene foam, mineral wool, polystyrene foam, fiberglass. The following nuances need to be taken into account:

  • Styrofoam and polystyrene foam can be easily cut to size and glued under the window sill without further finishing. In this case, the violation of aesthetics is compensated by insulation.
  • Fiberglass and mineral wool will have to be additionally sealed with plasterboard or the same polystyrene foam, since they have a loose structure. In addition, they can crumble and release small particles into the air that penetrate the respiratory tract. The advantage will be better insulation. The finishing material can be painted or wallpapered.

Insulation can also be done along the outer perimeter of the slopes, where they connect to the wall. The cracks should be cleaned of foam residues and sealed with silicone sealant. This measure will eliminate the risk of air entering from under the slopes in winter for several years.

Another option is to stick a special heat-saving film onto the frame. It forms an additional air pocket between the profile and the glass. This measure will not eliminate the penetration of cold due to the above reasons, but will serve as a means of retaining heat in the room. Installation is carried out in the following order:

  • The window frame must be washed with soapy water and degreased with alcohol or ammonia.
  • Apply double-sided tape around the perimeter.
  • Cut the heat-saving film taking into account the overlap with the glued tape.
  • Attach to the window, press tightly and heat the entire surface of the film with a hairdryer. It will stretch and become transparent.

There are films that can be glued directly to glass, but they do not form the effect of a third chamber of a double-glazed window and have less heat-saving ability. The insulation is installed in the fall and removed after the end of the heating season. It is impossible to use it a second time; you will have to find a new one. The presence of the film does not interfere with ventilation. Some owners cover the entire window opening with it, but then there is a risk of increasing humidity and deteriorating the quality of the internal atmosphere.

If you have any problems with the fittings or the correctness of the installation, you need to contact the installation company. The work will be carried out under warranty or at a reasonable price. It is always better to turn to professionals rather than experiment with dismantling on your own.

If the master or owner has eliminated all possible problems, and the next season the situation with window ventilation arises again, then there is only one way left - to replace the window structures. Modern windows are produced with automatic switching to winter mode and equipped with high-quality seals and fittings.

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