Measuring from the outside of the wall is more common.
But if there is an attic access, it can be done safer from inside the attic.
Once the old vent is out, the opening will be easier to measure.
There may be studs behind the opening.
Do not remove any supportive framing to install the new vent.
The wall thickness may determine the depth of the vent.
This picture may only accommodate a 1 inch or 2 inch deep vent.
If the opening area is clear, the depth of the vent does not matter.
Placing a 4 inch or even a 6 inch deep vent will be no problem.
Start with measuring across the base of the triangle opening.
Place the tape measure on top of the bottom board and measure from point to point.
This will be the width.
Now measure the center height from the top of the base board up to the center point.
On the order form these measures will be "opening size".
We will reduce these measures 1/4" per side dimension-ally for the vent to fit the wood opening.
On a triangle vent, this is not 1/4" per measure.
Do not add or subtract from these measures. It will hinder the install.
"Opening size" is usually for front flange and no flange vents that slide into an opening.
"Tip to tip" is usually for back flange and J channel vents mounting outside the wall.
For the measure to be considered "tip to tip", it is of the actual vent itself.
But only of the vent. Not including any flange or nail fin that may be added.
Hook the tape measure on one bottom corner of the vent and measure to the other corner for the width.
The center height is from the vent bottom (not flange) to the peak.
This is called a "tip to tip" measure.
The vent will be the measure ordered not reduced in size.
This is an old vent being replaced shown from the back.
The red line shows where the outer edge of the vent is for getting the width and height.
The louvers had almost closed up on themselves and he called it a Limpco vent.
One more potential triangle measure that may arise.
The off center triangle vent may be a 6/12 pitch on one side and 10/12 pitch on the other.
Stay with me for a minute and this will be understandable.
The width and height are still measured the same with the height being the tallest point. (red)
Now, measure from the left to where the center height was measured. (green)
And measure from the right to where the center height was measured. (blue)
For ordering, use the "comments box" and enter "off center vent, left half 24 3/4" right half 48 1/2".
Of course use the measures you gathered.
This will tell us the vent is wider on one side and which side.
The third dimension will be the depth.
The 1" triangle vent is 1" thick.
The 2" deep vent is 2 inches.
4" vents are 3 1/2 inches.
And the 6 inch is 5 1/2".
This is considered when evaluating the space available for the vent to protrude back into the attic beyond the wall thickness.
If anything was overlooked or left out, feel free to contact us via
phone 901.281.2887