Existing dry lined walls/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.
It is not advisable to lip the plasterboard face since this could lead to inadequate and unsafe fixing. It is also difficult to form a plasterboard opening which is fully squared and in one plane. The secondary window will accentuate any building tolerance.
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Guidance