Looking through the newly cut hole in the roof of our van conversion ready to attach the Thule Omnivent roof vent

The Ultimate Guide to Installing a Thule Omnivent Roof Vent/Fan

| Our Citroen Relay Van Build

We decided to install a Thule Omnivent Roof Vent and 12V electric fan in the roof of our Citroen Relay van conversion because after much research it seemed like a good idea for cooking, living, and general breathing in the van.

Looking through the bottom of the Thule Omnivent that we installed in the roof of our van conversion

Why Do You Need a Vent/Fan in a Van?

For one, we like cooking and want to ensure that the inside of our van stays nice and dry. So, the 12V Thule Omnivent roof vent/fan has a ventilation or extraction setting so you can extract the air when you’re cooking and ventilate the van on the warmer days. The second Thule Omnivent is a vent/skylight, which opens manually. This will help the circulate the air brought in by the fan, but it is also provides us with bonus natural light inside the van.

The Thule Omnivent Roof Vent comes with a built-in blackout cover for happy sleeping or a mosquito net option, so you can let air in but not the mosquitos, flies, or moths. (I hate moths.)

Which Vent Brand to Choose?

There are a few recommend brand names when it comes to fans and vents, so do some research and find the one for you, and that fits your budget.

There were a couple of thing we liked about the Thule Omnivent Roof Vent. Firestly, we could fit it to the roof with adhesive and mastic tape, rather than having to screw into the roof (one hole was enough), it was reasonably priced compared to some other options and they are a decent size to provide good ventilation and light.

Van conversion roof vent what it looks like from the top

Location, Location, Location!

Before you get crazy with the jigsaw, deciding where your Thule vents/fans are going to go is important. What other equipment is going on your roof? Are you having a roof rack? Solar panels? You don’t want to install your vents and then realise you forgot to plan out where your solar panels are going, or that you wanted a roof rack but now that won’t fit.

Measure your solar panels, vents and most importantly, your roof, then draw or design a roof plan, marking out where everything is going before you start cutting enormous holes in your van. You might also want to consider where your kitchen is going to be if a reason for having the vent or fan is to help extract when cooking.

Before Installation…

  • The Thule Omnivent Roof Vent comes in three pieces: the top, outside vent cover, the inside internal frame of the vent and then the inside cover. You will only need the top section of the vent and the internal frame for now.
  • You’ll need to build a DIY wooden frame: The vents used for van conversions are designed for a thicker roof, like a caravan. In order to be able to fit the outer part to the internal frame you need to make a simple frame. This frame will be sandwiched in between the two sections. Tom made ours using spare timber and pocket holes. It doesn’t need to look too pretty; it will be covered later by the internal vent cover. (For the 12V electric fan your frame will also need a hole for the wires to go through.)

Watch our video: How to Install a Thule Omnivent Roof Vent:

How to Install the Thule Omnivent Roof Vent/Fan:

  • Before you get on the roof, gather all your tools and equipment before you start so you don’t have to be going up and down the ladder.
  • Measure the vent (a million times) and then double check.
  • Hop on your roof (safely) and clean the area. Mark up where the vent is going to go with masking tape or Frog Tape and a fine biro pen. (You’ll know if your square is ‘square’ if when measuring across diagonally from corner to corner, it’s the same as your horizontal measurements. In the Thule vent’s case, it’s 402mm. Then double check your measurements… Yes again.
  • Using a punch (optional but recommended) and a stepped metal drill bit, make your pilot holes in each corner of your square.
  • Cut out the hole with a jigsaw*. Top Tip: Start at the furthest point so you can cut towards you and, if needed, you can lean on the panel. (*Some people use angle grinders to cut the holes, but others have argued that you shouldn’t because they spit out hot pieces of metal which can damage your paintwork. So, we went with the jigsaw.)
  • When cutting the last side, if you can, get someone to hold the sheet of metal  steady with plyers so it isn’t vibrating/moving around as you cut.
  • Peel off the tape and clean off any residue. Or use Frog Tape which is more expensive but saves you the job of cleaning the sticky residue off.
  • File any rough edges.
  • Clean the area that the vent is going to sit and the edge thoroughly with methylated spirits. Top Tip: Using latex gloves or similar for cleaning and after means you won’t leave any fingerprints or oil from your skin where you’ve just cleaned, which will ensure optimum adhesion of the mastic and adhesive.
  • Treat the exposed metal edge with Red Oxide paint and allow to dry.
  • Apply mastic tape. It’s quite fiddly stuff. We recommend wearing gloves and leaving one side of the peel-away sheet on until you’re ready to put the vent in, otherwise you may have dust and dirt getting stuck to it. (The Citroen Relay has a corrugated roof, we used it folded and layered the mastic to fill the grooves to ensure a watertight fit.)
  • Prepare the vent by sanding the area that is going to be stuck down, before cleaning it with meths. This will help it to adhere to the roof. (This can be done at the start, so it is ready for installation.)
  • Apply adhesive (we used Soudal Fix All) to the edge of the vent, ensuring there are no gaps at all.


  • Inside the van, attach your DIY frame and the internal part of the vent with the brackets provided with the vent.
  • Back on the roof – seal the edges of the vent with… You guessed it, Soudal Fix All.
  • Top Tip: Create a masking tape square around the vent. This will give you a clean edge. (Thanks to Our Wild Horizons for that great tip!)
  • Bonus Top Tip: Make a mixture of washing up liquid and water so you dip your finger in and smooth down sealant without it sticking to you.

That’s it, you’re done!

Once fully dry, test that the vent is watertight by spraying it with a hosepipe or in our case waiting for the rain and hoping for the best. We’ve left the internal cover off until we’ve insulated and finished the ceiling.

What do I need?

Here are some key products we used… (As an Amazon Associate I earn from qualifying purchases.)

Thank you for reading our blog, we hoped you enjoyed it and we certainly hope it was helpful. If you did, and you haven’t already checked out our other blogs, please stick around. Or find more videos on our YouTube channel, where you can leave your questions and comments and follow our van build series.


Do you need a roof vent in a van?

We decided that the more ventilation and light the better. Especially since we will be living in our van pretty much full time. We decided on two vents, one electric, so we could have ventilation and extraction whilst we’re cooking.

How do you stick the vent to the van roof?

We used mastic tape and Soudal Fix All to seal the edges. As well as the brackets and internal screws that come with the Thule vent. See our gear list above for the exact products we used.

Why do you need to build a DIY wooden frame for the fan/vent?

The wooden frame gives you a more secure fit and gives the screws a much deeper hold than if you were to fix it directly to your roof.

What is the best tool for cutting holes in your van roof?

We’ve seen many people use angle grinders and have been recommended to use one by someone, but we also heard that they can spit out hot flakes of metal which can get stuck to your paintwork and cause damage/rust. We’re not van conversion experts, so for us, ‘if in doubt play it safe’, so we decided to go with the jigsaw.  

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