Installing a roof mounted fan.
Before the rear bulkhead, before the shower and cupboard; the ventilation fan
has to go in. Scary moments a 350 mm square hole is to be cut in the roof.
Measure 59 times !
Maxxair is regarded as the best fan due to its reliability, noise levels and options to reverse, change speed levels and so on. Not wanting to take any shortcuts I chose this fan to install. At the end of the day, the price is a small part in the cost, given its exposure to the elements and long term use.
Nature had its say, thwarting installation many times. You can bet that if I make that cut, the 20%
chance of rain will be a winner. I had to wait weeks before there was a clear
cut opportunity. It gave me time to do many walkthroughs and full sized layout
modelling.
I chose a position in the rear as I wanted flow from the open sliding door
and/or windows. It was to be offset to allow for room should I proceed with a
shower or build a full sized cupboard. Much playing around too to give room to
the bulkhead separating the garage in the rear and roof struts. When I did
make a cut in the ceiling, much to my dismay the cupboards will be too close
to the cowling flange. Oh well, its only a bit more work
For the first time, I tried using the multitool. I did a test cut on the
ceiling plywood for the fan to extend through. I must say I am
impressed. No splintering of the wood. It worked well on steel sheet too, once
I got the right blade. Much better than a jigsaw.
I drilled a few holes up to proved an accurate location for a wooden template,
then taped the template to the top of the roof for marking out.
Nervous moments. I am cutting a dirty great big hole in the roof of my van.
After I cut the hole, I made sure to have a sufficient protection against the
elements whilst sealants cured or should the heavens release their fury.
It is imperative to ensure that the cowling of the fan is fully sealed, and
will be so for many years. I use a combination of a butyl mastic seal and
marine grade polyurethane sealant. Where the butyl layer is between the
cowling and the roof and the polyurethane sealant as a first line of defence
and UV protective layer on the perimeter. As the two are incompatible I
protected the outer layer of polyurethane against the primary defence butyl
layer with a silicone barrier to stop leaching.
It is probably an overkill to bolt the flange down with all that sealant, but
sealants can fail. Also there is a need to attach the inner cover, so there
are numerous bolts around the flange. These are all protected with a layer of
sealant against corrosion - stainless steel does rust !
The fan worked out to be in a good position, allowing for a shower to be
installed and providing ventilation in a dead air zone of the van. The
waterproofing worked out well, though I found in heavy weather that the water
pooled in the gullys between the ribs. In order to prevent overflow into the
top of the flange I hammered down some of the intermediate ridges and dammed
up a region before and aft so that the water will flow around the fan flange.
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