subject: Upvc window construction considerations [print this page] When buying new vinyl windows for your house there are many choices one of the most popular is the vinyl double hung or the double hung window .Lets take a closer look, the DH has a main frame and two operable double hung that operate in a up and down manner. For the most part the lower sash can be lifted up to open the window, or the top sash can be lowered down. Because you can't use both sash at the same time this type of dh allows for only half of the available area for ventilation this is some thing that could be a consideration when choosing a upvc window.
This window was designed to replace the original wooden double hung in older buildings it works well in window openings as old as two hundred years or as new as twenty years . It is a complete unit and has a built in balancer system to replace the original ropes and cast iron weights found in older houses. Not all vinyl windows are created equal if your thinking of investing in them for your house there a few points to consider lets start with the main frame again.
A fusion welded main frame and sashes, gives us a twelve point welded window which is of better quality and is highly suggested as a starting point. When examining a sample window take a look at where the two sashes come together in the middle, that's called the center rail they should both come together when the window is closed and locked. A simple test to check how tight the sashes come together is to open the bottom sash a couple of inches and insert a piece of paper between the two sashes, and then close and lock the window , then tug the paper to see how tight the two sashes lock together at the meeting rail, you should not be able to pull the paper out without ripping the paper.
Next look at the sill where the bottom sash closes. A regular window sill is pitched to allow for drainage but is also flat. When the bottom sash comes down to closed position the seal is made between the sash and the master frame by a piece of weather stripping called a bulb seal. Its what stands between you and the icy winter winds. There are a couple of weak spots with this design, if the window is installed out of square by a little as an eighth of an inch you could have a lot of air infiltration.Or if the bulb seal is cut a little short you'll have a draft.
And then there's security, because the sash sits on a flat sill, it is very easy to slip a crow bar under the sash and rip the sash open. But there is another choice its called a hospital sill why its called a hospital sill I don't know, but anyway as we mentioned in an earlier post when you weld a master frame you have to install a special piece to get the contour of the sill you need because as we explained in an earlier post you can only weld identical parts together. Some manufacturers use this situation to improve their design, the hospital sill is a u shaped channel which allows the bottom sash to be closed down into and below the surface. So if the window is installed a little out of square you still have plenty of protection against air infiltration because the sash is usually recessed by about half of an inch, and if the bulb seal is a little short you still have protection.
And finally security, the recessed design does not permit a crow bar to be easily jammed under the sash, having said that the issue of security comes up often with upvc windows lets keep it in perspective the chain is only as strong as its weakest link and that people is the insulated glass if some one wants to get into your home through the window their going to get in. If some one puts a crow bar under the sash of most upvc windows that lock will come right off. This sill design will make that very difficult to get the bar underneath the sash and if your sash has aluminium or steel reinforcing at the center rails the lock will hold much better so that leaves the glass... the weak link.
The biggest deterrent to breaking the glass is the racket, if your burglar doesn't mind making noise that's the easy way in. If you live in a high crime area or your just concerned about security look for that hospital sill design make sure that your replacement window has metal or steel reinforcing at the center rails that's where the locks are installed and you could ask about things like security laminated glass, double strength glass which is stronger than standard glass. Up grades like that are usually very expensive Your money may be better spent on an alarm system or security grates for the windows.
A moment ago I mentioned reinforcing the meeting rails, that's not some thing that comes standard. Some replacement windows come with no reinforcing any where. Depending on the size of your existing window openings, its some thing you may need to consider, there are some manufactures that reinforce the four sides of the master frame and all sides of both sash. under normal situations that might be a little bit much. If you start with a solid, welded main frame it should be fine with out reinforcing, the sashes on the other hand should defiantly be reinforced for several reasons. Number one to mount the locks on to the sash ,number two while the master frame doesn't move after installation, the sashes are always being shoved and pulled up and down and because the frames of the sash are much smaller than the master frame they can be effected by the sun sagging over time.
