Double glazed units into single glazed wood frames- plan OK?

[Grampian]

I have a number of non-opening windows with single glazing which I'd like to replace with double glazed units. There are various reasons for this but it is in part due to one or two sections starting to rot on the lower frame where condensation has accumulated.

I am thinking I can remove the glass and run a router & chisel around the frames to increase the rebate and remove the rotten wood. I would like to then install a 20mm overall double glazed unit. As far as I can tell they can be positioned on top of 5mm thick packers and stuck to the inner face with glazing tape. After this install new exterior wood bead and run some sort of (silicone?) sealant around the gap.

Diagram of the above:

Untitled

• Grampian
• 30 May 2015
• 1

Does any one have any comments or suggestions on the plans? The windows do not get a lot of sun or rain on. It would be my biggest/most terrifying project to date so I am keen to avoid nasty surprises!

 

[Gazman16]

How deep can you route out and how deep are your beads?
Ideally you need 5mm clearance all the way around the unit for airflow/ventilation and the beads should completely cover the seal and spacer bar to protect them from the elements so around 17mm deep at least is what you want.

Dont forget drainage slots at the bottom too. Without these steps you could end up replacing some/all units every few years.

 

[Gazman16]

Are you against changing to PVC windows seeing as you already have some rot creeping in? The glass units are around 60% of the cost of whole windows.

 

[Grampian]

How deep can you route out and how deep are your beads?
Ideally you need 5mm clearance all the way around the unit for airflow/ventilation and the beads should completely cover the seal and spacer bar to protect them from the elements so around 17mm deep at least is what you want.

Dont forget drainage slots at the bottom too. Without these steps you could end up replacing some/all units every few years.

There is ample wood in the existing frames to take away the required amount. They are over 9cm thick and the existing rebate is around 3cm. Similarly the depth looks more than enough.

I was planning on using a few 5mm spacers as labelled in the diagram, and I'll be replacing the beads and adding some small ventilation slots on the lower edge.

 

[Grampian]

Are you against changing to PVC windows seeing as you already have some rot creeping in? The glass units are around 60% of the cost of whole windows.

- Architecturally / aesthetically the building suits wood (although plastic would look about as acceptable here as anywhere).
- Restrictions are also in place on the property and replacement frames would require approval (with associated costs) and FENSA certified installers, merely replacing glass avoids this.
- The proposed work also seems within my capability.
- I am not going to be replacing all the windows and it will look undesirable if only some are PVC.

 

[crank39]

As Gazman says dgus really do not like timber but it looks like you have done lots of research into this and have all the bases covered so yeah why not give it a go, the main thing is they must have some form of drainage below the unit and under the bottom bead to let any moisture out

Sounds like a nice project to do in the summer months

 

[Grampian]

As Gazman says dgus really do not like timber but it looks like you have done lots of research into this...

Thanks, I'm hoping it's not too tricky, just trying to determine if I need a particular sort of sealant for the outer face. Seems like some silicone based stuff will do.

Sounds like a nice project to do in the summer months

Hope so, just got to figure out how I can use the router correctly on the frames in situ. I'd like to use the inside edge of the frame as a guide but will need to check it will work. What could possibly go wrong!

 

[crank39]

If your going to use a silicone sealant keep it away from the hot melt or polysulphide that seals the unit, it'll attack it and the unit will break down anyway and render all your other hard work to get the unit to last pointless, get one that is suitable for glazing

As for routing the frames, the only issue I see is not being able to get right into the corners so some finishing off by hand with chisels will be required.

I have a Makita laminate trimmer with is basically a miniature router, this would be my tool of choice for this job, it would allow you to get closer into the corners for less hand work

 

[ronniecabers]

If replacing glazing in wood , we normally apply the glazing tape to the internal rebate and then externally for the bead to fit against. If you so wished , after this you could apply a thin bead of silicone....whatever you decide , make sure to use Low Modulus silicone , any others attack the actual sealed unit hotmelt/polysulphide

 

[Grampian]

If replacing glazing in wood , we normally apply the glazing tape to the internal rebate and then externally for the bead to fit against.

What tape thickness do you use for this? I'm guessing it's dependent on a number of factors. I was looking at 3mm - does it compress a bit to take up imperfections?

 

[ronniecabers]

Does depend, but yes does compress

 

[crank39]

As your making your own rebate you have a choice of thicknesses but 3mm would be acceptable.

As for compression well you can compress the tape between your fingers quite easily giving the impression its quite soft but trying to compress a whole line of it with a dgu its actually quite difficult, at a guess 3mm would only compress 1mm if that