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Tips & Advice

8 min read

How to install a window – step by step DIY guide

Written by

Agata Gniady - Tęgi

Reading Time: 8 minutes

There comes a time in your life when you have to replace windows in your house. Generally, it happens when you observe one (or a few!) of these signs. However, it may also be just the need to update your window’s style and function and, so to say, increase the value of your property.  But whatever the reason, you may be looking to learn how to put in new windows. And like with many home projects, you can opt to do it yourself window replacement and do not necessarily require a contractor to get it done right. In this article, we’ll show you how to install new windows in the house and, what’s even more important, how to conduct DIY new window installation smoothly and successfully. 

Can I install replacement windows myself?

The answer to the above question goes as follows: yes, of course you can! You just have to make sure that you’re following all the important guidelines and instructions regarding installing a new construction window in an existing home, using all the specific accessories and methods. As long as you follow these instructions as a professional would, you are perfectly fine with doing the work yourself. Apparently, when you decide to install new windows, costs play a decisive role in your decision. You want to save money on labour expenses related to professional window installation (check HERE for more information). But while DIY new window installation can save you money on labour costs, you’ll need to invest in materials and tools. So before asking “How do you install a new window?”, better ask yourself what equipment is needed for correct window installation. High-quality, purpose-built tools are the key to your do it yourself window replacement success. 

Aluminium windows Genesis

Undeniably, tool or material requirements will depend on the complexity of the installation and whether it is a new house window installation or the process of installing a new construction window in an existing home. In our opinion: the upfront investment in good tools will always pay off!

Tools and materials required:

  • Hammer drill;
  • Metal anchors;
  • Expansion bolts;
  • Screwdriver, hammer;
  • Screws;
  • Cordless drill/driver;
  • Bubble/laser level;
  • Mounting foam;
  • Mounting plates;
  • Hand or electric saw (for wooden frames);
  • Crowbar extractor for nails;
  • Backing boards;
  • Safety glasses;
  • Construction cut-resistant gloves 
  • Tape measure;
  • Masking tape;
  • Flashing tape;
  • Caulking;
  • Drop cloth.

Obviously, as Fenbro window fitters say, all the mentioned tools have to go in pair with your strength and positive attitude to the challenge that is awaiting you. It is clearly a good idea to plan your work and divide your DIY new window installation into phases. Installing a new construction window in an existing home is a serious project and as such, it requires good and precise planning of the individual work steps. This will make it easy for you to coordinate the whole project and achieve the set goal successfully. 

What is the best way to install replacement windows?

Frankly, it would be perfect to have one clear answer to the above question. However, installing new windows in the old house (as well as in the new one) is a complex task and in order to lead it to the final success, it is crucial to perform all its phases meticulously and in accordance with general principles of construction art. In order to successfully install new windows in house, one  should always adapt the whole process to the type of joinery and the specific nature of the investment. The key to success is always to properly measure the window. If the measurements are taken correctly, then the whole do it yourself window replacement will be much easier and more effective.  You do not want your newly bought windows to turn out too small or too big in relation to the window opening, do you? Measurements should be taken very carefully with a tape measure and a level. You should measure the window frame on both sides (outside and inside), and you should also make sure that the angles of the window opening are actually straight. If you want to get some more precise tips on how to correctly measure windows, check THIS blog article written together with the Fenbro window expert. If you are 100% sure that the window dimensions correspond to the window openings, you can follow with the further steps of DIY new window installation. Here are the phases of the window installation process:

  • Removing the old window 

Break the seal of the paint and caulk with a utility knife to make removing trim easy. Start by removing the interior stop moulding, supporting the window as you go to ensure it doesn’t fall out of the opening. Next, remove the sashes from the frame and then the fasteners holding the frame to the opening. Remove the frame from the opening and afterwards, remove any fasteners and shims left in the opening.

  • Preparing the window opening for the installation of new windows

Thoroughly remove the old insulation and clean the window opening of any residues, dirt and impurities. Remove any brittle parts of the wall and crumbling plaster. Thorough cleaning of window openings will prevent the so-called thermal bridges through which heat escapes. Sealing materials adhere better if the hole surface is primed and moistened.

  • Mounting the window

After the preparation of the window opening is completed, the window is inserted into it. At the same time, the window itself is centred horizontally and vertically in the opening. Use a bubble/laser level to ensure that this stage of installation is conducted seamlessly.

  • Installation of anchors

The anchoring method provides the structural strength to securely install a new window in a wall. To mount the window in the reveal, you will need properly attached dowels or anchors, which should be placed at a distance of about 20 cm from each corner.

  • Installation of the window fittings and handles

This stage ensures the aesthetics and functionality of the windows. Choose only original fittings and handles for your do it yourself window replacement, as the service life of your windows depends on it.

  • Window sealing

It is surely one of the most important activities in the entire window replacement and installation process. Good sealing is the basis of thermal insulation. For this reason, it is necessary to use good quality polyurethane foam. The latter is a type of insulation material and sealant that can be used to fill gaps and effectively install new window in existing wall. It creates a strong, watertight seal, preventing water and air from entering an area. Using polyurethane foam sealants helps to maintain a more comfortable indoor temperature and prevent warm air from escaping during cold months.

  • Installation of inner window sill

It is a multi-stage process, including measuring and cutting window sills (depending on window sizes) and fastening them to the window. The width of the window sill largely depends on how much space you have – generally, window sills are 3 to 5 cm wider than the window on each side. Apply glue (preferably polyurethane adhesive) to the sill and wall, slide the sill into place, secure with wedges, and level with a bubble/laser level. Afterwards, when the glue dries, fill gaps with silicone, trim excess with a knife, and use putty for any wall defects.

  • Carrying out finishing works

It basically means levelling the surface of the window reveals with putty and sealing the joints with silicone mass.

uPVC Windows IDEAL 8000

How should replacement windows fit?

It is clear that DIY new window installation is a serious undertaking – and as such, it raises many questions and doubts. It can be a stressful task if you do it for the first time. But, luckily, you don’t have to go it alone! In this article, we’ll provide you with all the information and knowledge you need to make an informed decision about do it yourself window replacement. We asked our best window fitter in Ireland some most important questions on how to put in new windows – and here’s what he told us!Read on now to learn more – and get ready to install new windows in the house like a pro.

Do you install replacement windows from the inside or outside?

Typically, windows are installed from the outside of the building. But it all depends on what the specific building allows. If it is a new construction, the windows are installed from the inside of the house. If it is a renovation project, we generally should install windows from the outside.

How to prepare window openings before DIY new window installation? What are the effects of improper preparation of the window opening?

The window opening should be properly cleaned and widened at all times. It should be properly carved out in advance so that there is no need to correct anything during the window installation itself. You should not hammer anything after installing a new construction window in an existing home, as the window may get damaged.

Can I change the size of window openings before installing the window?

Yes, of course you can. However, it requires much more preparation work and it’s more time-consuming. You can both increase and decrease the window opening size, obviously within reason. There should be no problems with changing the size of window openings while installing a window in an existing brick wall or a timber wall. The only obstacle is steel structures – in their case,  modifying window opening sizes is impossible. 

Where to place the fixing points?

Typically, the fixing points are placed in the upper, middle and lower part of the window. In the case of a double-leaf window, it is also a good idea to place a fixing point on a post (both the top and bottom one). Generally, the more fixing points there are, the more stable the window is going to be.

What is thermal installation and why is it used?

Thermal installation involves maximal window sealing. Instead of mounting foam, we use tighter expanding tapes or vapour permeable tapes, which allow steam to pass through, but not air. However, the use of a thermal window sill is also crucial here – thermal installation will not be effective if the bottom of the window is placed on a concrete window sill. Such a cold pit will automatically become a thermal bridge. To prevent this, thermal installation must go hand in hand with replacing the external window sill with the so-called thermal window sill. Thermal installation certainly makes sense when insulating a whole house. Otherwise, it is pointless – installing warm windows will not help if the building walls allow heat to pass through. And it should be noted that the thermal installation costs are much higher than in the case of standard installation. So summing up, thermal installation is generally recommended in new buildings, and not in house renovations.

How are energy-saving windows installed?

It is known that even windows with the best parameters will not fully fulfil their purpose if they are installed incorrectly. Therefore, energy-saving windows are installed using the previously mentioned thermal installation method. Such windows should be mounted on thermal window sills and warm foundations. Only then does the use of energy-saving windows make real sense.

What are the most common mistakes when installing windows?

One of the most common mistakes is the lack of proper verticals and horizontals. This means that the window does not function properly and after a few years, the hinges, frames and sashes may bend and, as a result, the window no longer has its original tightness. Another mistake is improper window sealing, which results in heat loss and draughts.

What should you always remember about when installing windows?

When you install a window in an existing wall, always remember to maintain the correct verticals and horizontals of each plane and properly seal the window. Even if you use only mounting foam for the latter, remember to apply it thoroughly all around the window. I do not recommend using expanding mounting foams for window sealing, because they can lead to excessive window frame expansion and as a result, the window won’t function properly almost from the very beginning. 

Conclusion 

Has our DIY new window installation guide proven useful for you? If yes, then great! We hope that installing a window in an existing brick wall is no longer a subject that scares or overwhelms you. However, if you’ve come this far and decided that it’s not for you, don’t worry! Go to THIS website to learn about trusted window installers in your area in Ireland and the UK. You can always check the results of Fenbro building projects HERE – impressive, aren’t they? Our experienced window fitting teams offer top-quality new house window installation and know the best way to install replacement windows, too. Contact our Sales Team and ask for a sales and installation quote!

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