Fensa Poor uPVC installation. Expert advice and 2nd opinion please?

11 Nov 2020
Reaction score
United Kingdom
Hi, I would be grateful for some advice and clarity on a window installation that was completed at my house. Since installation we have had beads whistling, issues of water ingress on various windows and a door, which after layman consumer research I believe highlight a lack of fundamental installation good working practices. The installer has reacted to these issues in a timely manner but we feel the remedial works are "bodged", make do fix's that are insufficient and if the original installation were done properly would not be required.
Fensa have been no help at all, as the installation is over a year old.

Q1: Is it a Fensa or Building Regs requirement that silicone is applied between element and sill upstand?

Q2: Should a bed or foam fill be used to make up gap beneath external sill and outer block work?

Q3: Should fixings be within 150mm of corner welds?

Q4: If not does this potentially affect warranty?

Q5:What is the means of rectification?

Original installation

We had the replacement of 10x upvc windows and 1x upvc door completed by a Fensa registered installer and were pleased with the installation. As we had ongoing renovation works planned throughout the house it was agreed that windows, external sills and internal plastic sills were to be fitted but internal making good of reveals was to be done by ourselves.

Kitchen door
Kitchen upvc door: Issues with water pooling in frame and ingress from sill edges and where screws are protruding through bottom of sill. Installer's remedy was to check drainage wasn't blocked, make some adjustments to mechanism to tighten against outer seal and fit a "make do" threshold strip to rear of frame.

Kitchen upvc door: Water ingress still at base of door. After 3 visits from the installer and various methods to attempt to remedy including screw cap's and silicone in various spots on outer sill. Final word was that- due to the height of the step outside, moisture was being drawn in from the outside (why was this not recognised on the original installation?) It was suggested that I retro fit a DPM between the door and kitchen floor.
I have since noticed the following:

  • The sill has detached from the frame and is sloping backwards
  • Bottom of frame flex's due to lack of bedding
  • Fixings being less than 100mm-150mm from corners questionable
  • Lack of silicone between element and sill/lack of troughing

Bathroom windows
Since the original install our 2 x bathroom windows had internal plastic sills and plastic strips on the reveals. We are currently in the process of having our bathroom re-fitted. This involved removing the plastic internal sills and having the entire room re-plastered. After a rainy and windy night we noticed moisture appearing on one of the reveals, this ingress would not have been revealed if the plastic non porous sill was still in situ. Please note that there is no bridging of the cavity due to plasterboard, bonding or muck.

I cut out the area of wet plasterboard an image to a third party professional window fitter for some initial advice and he said "it looks like he hasn't troughed the end of the sills properly"


I contacted the original installer and he came along with a roll of damp proof membrane saying " your outer cavity wall will be wet anyway so this will stop any moisture transferring to the inside when I put this between the outer and inner wall".

My reply was "no, my cavities should not be wet as I have loose fill cavity insulation, and fitting the DPM will just be a sticking plaster over a poorly sealed window. The reason I had all my windows replaced was to stop water ingression".

I asked the fitter if he had ran a silicone bead between the element and sill upstand on installation. He replied "Yes I have done that but if there is a small gap or break water will get in".

The installer then made the following attempt at rectification:

  • Squirted silicone into the corners of the reveal
  • Cut out a strip of plasterboard along the back edge of each window and filled with silicone to provide a barrier
  • Squirted silicone from the outside into the corners of the drainage channels (on a new installation I do not think this is acceptable and looks shoddy)
Since the installers remedial attempt water is still entering the cavity via the sill edge.

This led me to seek a second opinion from a friend who is window fitter who came to my house to visually inspect the installation. On a couple of the windows where the reveals have not yet been fully finished he managed to get his fingers into the end of the sill to check if he could feel any silicone trough application, he couldn't feel any.

He also pointed out the following:
  • Lack of bedding or foam fill to windows (able to get hand all the way under some of the sill's from the inside)

Image shows outer skin brick, with gap between sill. This is continuous for the length of window.
  • Fixings being far less than 100mm-150mm from corners on many frames
  • Suspicion that sill's have been insufficiently "troughed" with silicone or not at all. (This could be the case for every other window, but moisture is not showing due to plastic internal sill's still being in situ)
Recently I decided to remove a small window to check if the installer had siliconed between the element and sill. It turns out he was lying to me. Please see next image:
Sponsored Links

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links