I'm building a house in Portugal have just visited to find some double glazed units have been joined simply by putting a mastic type substance between them. I have 3 expanses of glazing each 2.4m high and ranging from 3m to 4.5 meters wide. I was expecting single units in each opening. However, in 2 cases there are two units and in the largest opening (4.5m) there are three. The surround of the opening has an aluminium frame but the join between the units is simply filled by a mastic type substance so you can see the black and silver edge of the sealed unit. It is not just unsightly, It doesn’t seem safe to me. The windows seem to flex terribly and although the frames are not secured properly yet, I am worried that this still won’t be safe even when finished. The builder & architect seem to think this is acceptable and common practice. I have since seen a lot of SINGLE glazed tempered glass joined in this way but no other double glazed units. With the single glazing (on shop fronts etc) the join uses clear mastic and as there is no silver or black like in the double glazed units, this is not unsightly. It does flex but seems quite strong and is used in many places (in Portugal). Can anyone advise on whether there is a standard which prevents this type of join on double glazed units either in the UK or Portugal and any advice generally on what should be done with this sort of join/large opening would be extremely welcome. Thanks JDSE

JDSE,

It is possible to get a two part " H " section fitting for joining two panes of DG units. The " H " section comes apart, one piece is placed between the DG and other capping piece screwed on top. The unit does hold the two sheets of glazing apart slightly, so your sizing may be off, but it hides the join. I can't vouch for efficiency or load bearing etc, etc of the product, you would have to contact manufacturers, but I would think it's better than looking at exposed spacer bars.