FAQs

All you need to know about secondary glazing

Allowing for curtains, shutters and blinds

Yes you can. However; timber shutters generally close tight to the outer window and unless the whole shutter assembly is moved forward to accommodate the secondary glazing, they will cease to function. They should be sealed and fixed shut using packing timbers and insulation material as necessary, allowing the secondary window to be fitted to a vertical frame member of the shutter. Avoid fixing across the panel.
Can shutters work with secondary glazing? Can timber shutters work with secondary glazing? The preferred location and operation style of the secondary glazing may affect the positioning of blinds and curtains which, if existing, may have to be relocated or even replaced. Some windows are fitted with blast curtains and in these cases the client’s security adviser would have to be involved. Yes it is possible to have controls pass through the jamb of the secondary glazing but consideration needs to be given to the type of control e.g. wand, cord, or turn knob and assess whether an enlarged timber ground is needed to house the control and allow access for operation.
What about blinds with remote controls?
Additional image - What about blinds with remote controls?

Building features

Secondary glazing is only suitable for treating french, patio, balcony doors etc. typically those which are used occasionally for access to an enclosed area. They are not suitable for treating front doors or main access to an enclosed area. They are not designed to be operated from the outside.
Double doors can be fitted with either side hung casement or horizontal sliding units. Single doors can be fitted with side hung casement units.
If the doors are inward opening, then full consideration needs to be given to clearances and it may be that the primary doors will no longer open to 90°.
Is secondary glazing suitable for fitting to doors Existing dry lined wall/reveals should be carefully examined to locate battens for key fixing points. Plasterboard fixings should be used at intermediate positions. Side hung units require particularly sound fixings at the hinge point and an enlarged structural timber sub frame may have to be considered to provide this strength.
The design of any new dry lining should take into account the fixing requirements of the secondary window frames. A suitable steel channel or timber section acting as a sub frame should be set behind the plaster board at the fixing point off the secondary glazing where load is to be transferred. This sub frame may have to be tied back to the structure which is particularly important if side hung secondary windows are specified.
Can I fit secondary glazing on dry lined wall? Yes, but only at mullion points. When designing a treatment for ribbon windows consideration should be given to the future use of the space. If further portioning is likely, then breaking down the run of secondary to smaller units with more mullion points may be prudent.
How do partitions affect fitting secondary glazing Yes, ideally the suspended ceiling bulk head needs to be finished within the window reveal and provide a suitable fixing position for the secondary glazing. If the suspended ceiling extends only to the wall face, then a timber batten can be added to the rear of the bulk head.
Consideration must be given to the acoustic integrity of the bulk head, to avoid noise break through from the ceiling void.
Can secondary glazing be fitted to the underside of a suspended ceiling? Yes, trickle ventilators can be fitted to most secondary glazing, but consideration needs to be given to a number of factors: - Is there a trickle ventilator fitted in the primary window or sufficient air leakage in the primary window to ensure sufficient ventilation of the cavity to the outside?
- The fixing arrangement of the secondary glazing may restrict how a trickle vent can be accommodated.
- Avoid fitting trickle vents in the secondary glazing where there is insufficient or no ventilation through the primary window as warm moist air entering the cavity from inside the room is at risk of being trapped and may create condensation in the cavity.
- Is there a ventilation strategy for the room or building? Consider a comprehensive approach to older buildings where there is often sufficient natural leakage via ill-fitting components in the structure, fireplaces/ chimneys etc. What are the primary windows, how efficiently do they seal.
- Consider fitting extractor fans in high moisture areas like kitchens and bathrooms and how they would function i.e. humidity controlled, independently switched, extended timing when linked to lights, all to ensure the moisture levels in high-risk areas are controlled etc.
- If the secondary glazing is for noise insulation, consider the impact of fitting trickle ventilators reducing performance as we are introducing a hole in the secondary glazing. Acoustic ventilators may help mitigate some of this reduction in performance. However please note that acoustic trickle ventilators increase in size and protrude both into the room and the cavity.

Dealing with obstructions

The answer to this depends on many factors including; primary window clearances and styles, reveal conditions, appetite for the acceptance of restricted opening and the appetite for acceptance of structural modification.
It would be best to contact us directly to discuss your requirements and possible solutions.
My windows open inwards can I still have secondary glazing?Additional image for - My windows open inwards can I still have secondary glazing?Additional image for question - What about external windows that open inwards? That will depend upon the projection of the primary window hardware and the available reveal. We often find in these situations that the primary hardware needs to be modified or removed to enable a secondary glazing treatment.
Will hoppers and folding stays prevent the installation of secondary glazing? Ideally extractor fans should be removed and the primary window made good, as it will severely affect the performance of the secondary window if it remains.
If however, the vent is required and secondary glazing is to be installed, then a suitably matched secondary vent should be fitted in the secondary glazing adjacent to the existing - see below.
Do we have to relocate extractor fans to fit secondary glazing?Additional image - Do we have to relocate extractor fans to fit secondary glazing This question is particularly relevant to vertical sliding secondary glazing as the stop positions on the balances will limit the travel, which in turn can limit access. The extent of the limited access will be dependent on the depth of cavity and how close the break line is to the centre.
What happens if window handles get in the way?

Frames and cills

An odd leg frame and timber ground arrangement allows out of square openings to be dealt with discreetly. Enlarged or tapered grounds can be used to provide a true opening into which the secondary glazing is fitted. The enlarged timber grounds are finished to match the secondary glazing frame colour so that they blend in and require no post installation finishing.
How much tolerance is there for frames that are out of square? The cill should support both the weight of the secondary glazing and of window cleaners without deflection. Large sliding panels could weigh more than 30 kg per meter run.
Any movement of the cill will reduce the sealing efficiency of sliding panes and at worst, allow a panel to fall out of its frame.
Deep cills or cill casings having cut outs for air grilles must have sufficient supports or inherent strength to accept these weights without deflection. Air grilles may also have to be repositioned to avoid them venting into the cavity formed by the secondary glazing.
Are there specific requirements for the window cill? The odd leg frame and timber ground arrangement allows for splay openings to be dealt with discreetly. Splayed grounds can be used to provide a true opening into which the secondary glazing is fitted. The enlarged timber grounds are finished to match the secondary glazing frame colour, so that they blend in and require no post installation finishing.
How do we work with splayed reveals? The odd leg frame and timber ground arrangement allows the use of faced fixed joinery sub frames to create a reveal. The face fixed sub frame is fully factory finished to match the secondary glazing frame colour and requires no post installation finishing.
If there is no or minimal reveal, how do wen fit secondary glazing?

Condensation

Will secondary glazing help eliminate condensation?
In most cases, secondary glazing will help stop condensation, but this cannot be guaranteed. Adding secondary glazing will typically reduce the amount of warm damp air getting to the face of the primary window and this helps reduce the likelihood of condensation. However, it will also lower the temperature of the inner face of the primary window and if warm damp air is trapped within the cavity or if poorly fitted secondary glazing allows warm damp air to enter the cavity, the lack of air circulation can exaggerate/exacerbate the development of condensation.
In the fight against condensation it is important that the secondary glazing is well sealed and reduces the passage of air into the cavity from the room side to a minimum. But it is also important that some air is allowed to leak into the cavity from the outside. This can be achieved, in most situations, by leaving the primary windows unsealed.
I have secondary glazing and get condensation - what can I do?
Condensation occurs when warm moist air comes in to contact with a cold surface. Warm moist air can exist within the cavity between secondary and primary glazing due to;
  • The secondary glazing being opened and closed without ventilating the cavity air to the outside before closing
  • A fault with the secondary glazing seals
  • A fault with the building fabric
  • The secondary window left ajar allowing warm air to enter the cavity
Condensation can typically be cleared by ventilating the cavity between the secondary and primary glazing to the external of the building. i.e. leave the primary window ajar and close the secondary glazing, normally it will clear within the hour and the primary glazing can then be closed.
If the problem persists or returns, then you need to check for faults. Is the secondary glazing functioning correctly, are the seals all in place and are they engaging properly? Is there any damp entering the cavity through the primary window or reveals?
If there is nothing obvious, then it may be necessary to introduce permanent ventilation through the primary window frame (this can sometimes be achieved simply by removing some of the perimeter seals around the opening elements). Is the window timber framed – if so you can introduce small weep holes.

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