PVC windows and doors must be milled with drain holes in order to be watertight so that the accumulated water inside the windows and doors could be drained outdoors. In order to guarantee a smooth drainage of rainwater in the drain cavity, the upper or vertical side of the windows and doors must be milled with air equalizer holes.

Based on their locations and functions, the drain holes and air equalizer holes could be classified as interior and exterior drain holes as well as interior and exterior air equalizer holes. The specification and dimension of drain holes and air equalizer holes are shown in figure 1-6

The normal size of drain holes is ¦µxL(5mmx30mm)
The normal size of air equalizer holes is ¦µxL(4.5mmx30mm)
Special attentions should be paid when machining interior and exterior drain holes on windows and doors:

1, Do not dig through the drain cavity and steel reinforcement cavity in order to prevent the rainwater from coming into the main cavity and corrode the steel reinforcement.
2, Select the lowest position at the profile¡¯s drain cavity when making interior and exterior drainage holes to prevent accumulated water inside the profiles. The interior drain holes should not face directly with the exterior ones and they should be distributed alternately, as shown in figure 1-7

Drain holes and air equalizer holes must be milled under following conditions:

1, All exterior windows and doors in exterior walls must have drainage system
2, The profile for lower frame of each glass on exterior windows and doors must have interior and exterior drainage holes. The profile of upper frame of each glass should have air equalizer holes and also inside of it.

I, Quantity and distribution of drain holes
The quantity and distribution of drain holes are recommended as follows:

1, When side length of the lower frame is ¡Ü700mm, make an exterior drain hole exactly at middle of the side.
2, When side length of the lower frame is between 700-1800mm, make two exterior drain holes, at 1/4 of the side from the two ends respectively.
3, When side length of the lower frame is ¡Ý1800mm, make three exterior drain holes, among them two are at 1/6 of the side from the two ends respectively and the third is in the middle of the structural member.

Generally, one exterior drain hole corresponds to one interior drain hole, Due to the limitation by their fabrication size, the sash of casement and sliding windows and doors may only have one interior and one exterior drain hole at the structural member beneath it.

The quantity and distribution of drain holes are determined by the weather and rainfall in this region. More and bigger drain holes are required in the region with more rainfall.

II. Quantity and distribution of air equalizer holes

Each glass installed directly on the frame and sash of door and window should have one or more exterior air equalizer holes and one interior air equalizer holes milled at outdoor side of the upper frame. The interior and exterior air equalizer holes could face each other directly.
The milling of drain holes and air equalizer holes is shown in the following figure.

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