Over head

Here’s the catch on re­plac­ing a car­a­van or mo­torhome roof hatch.

Motorhome & Caravan Trader - - Tech Talk - Philip Lord

Roof hatches can be eas­ily dam­aged or, like any­thing fit­ted to the roof of a car­a­van, even­tu­ally prone to wa­ter leaks. This hatch is on a mo­torhome, but the prin­ci­ple is the same for a car­a­van, the only dif­fer­ence be­ing that here we’ve got a 1.2mm-thick sheet­metal roof and on a car­a­van it’s typ­i­cally a 0.7mm-thick alu­minium roof.

The hatch unit it­self here is the type with an in­te­gral ex­haust/in­let fan, but for the pur­poses of hatch re­place­ment there’s no dif­fer­ence be­tween this and a stan­dard non-fan hatch, ex­cept for the need to hook up two wires in this case.

This hatch had a cou­ple of prob­lems that caused it to al­low wa­ter to leak through. The plas­tic frame had cracked in two spots and the foam seal used was in­tended to take up the gaps caused by the ribs in the roof panel, but it ac­tu­ally worked as a mem­brane trap­ping wa­ter. Both prob­lems even­tu­ally al­lowed wa­ter through, stain­ing the ply pan­elling in­side. Luck­ily it was caught fairly early, or the time-con­sum­ing (and ex­pen­sive) job of re­plac­ing rot­ted in­te­rior ply would have been added to the job card.

Get­ting up on the roof of a car­a­van can end up in dis­as­ter, and that’s not just if you were to fall off.

Take care with these types of projects as you don’t want your hand­i­work to cre­ate fur­ther op­por­tu­nity for wa­ter leaks!

First, the screws se­cur­ing the hatch to the roof are re­moved. Then the hatch assem­bly can be prised away from the roof panel. The hatch we were work­ing on was lifted off eas­ily be­cause the seal was so poor, but of­ten they can be dif­fi­cult to re­move. Don’t use metal im­ple­ments (screw­driver, scraper, etc.) be­cause they’ll dam­age the roof. In­stead, use a plas­tic chisel or a bev­elled edge strip of per­spex to break the seal and to gen­tly prise the hatch off.

Then it’s time to clean up the old seal and/or silas­tic, first ap­ply­ing wax and grease re­mover to soften the re­main­ing seal and then ei­ther a plas­tic scraper or a ny­lon brush drill at­tach­ment. A fi­nal wipe over with wax and grease re­mover, and the roof is ready for the new hatch.

The hatch needs to be prepped, firstly by sand­ing the smooth plas­tic so it’s rough enough for the silas­tic to bond to it. The fas­cia cov­er­ing the hatch sur­round on the ceil­ing will also prob­a­bly need to be trimmed.

This con­ver­sion didn’t have any re­in­force­ment brac­ing be­tween the roof panel and the ceil­ing ply lin­ing, so to en­sure that the new hatch re­mained wa­ter­tight, tim­ber brac­ing was added.

Now silas­tic can be added to the new hatch. We’ve used a non-acidic silas­tic to en­sure that cor­ro­sion is kept at bay. The trap here is to not use enough silas­tic – the ex­cess can be wiped off and, if you use too lit­tle, it can come back to bite you with fur­ther wa­ter leaks.

The hatch is then placed on the aper­ture on the roof and gen­tly pushed down so that the silas­tic makes a good seal.

Then the roof can be se­cured with, in this case, stain­less steel self-tap­ping screws. Stain­less screws don’t rust and so, again, help to avoid cor­ro­sion.

The ex­cess silas­tic is then wiped off, first by spray­ing a de­ter­gent/wa­ter mix so that the silas­tic ex­cess is more eas­ily re­moved and doesn’t stick to the sur­round­ing roof panel.

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Left: Like any­thing on the roof of a van, hatches can be prone to dam­age or leaks. Above: The roof ma­te­rial of a mo­torhome is gen­er­ally dif­fer­ent to that of a car­a­van, but the hatch re­place­ment process is es­sen­tially the same.

2 Re­move the old hatch. 3 Re­mov­ing the hatch unit reveals the foam gas­ket that al­lowed the unit to leak and the lack of brac­ing be­tween the roof and in­te­rior lin­ing.

1 Wa­ter stain­ing on in­te­rior ply due to the hatch leak­ing.

4 Ap­ply thin­ners to soften the old gas­ket ma­te­rial. 5 Clean up the con­tact sur­face with a plas­tic wheel.

8 Sand the new hatch plas­tic so that sil­i­con will key into the sur­face.

6 Do a fi­nal wipe down with wax and grease re­mover.

7 Fit a tim­ber brac­ing be­tween the roof and the in­te­rior lin­ing.

9 Ap­ply non-acidic sil­i­cone to the new hatch.

10 Hatch is placed over the aper­ture. 11 Hatch is se­cured with stainelss steel screws.

The ex­ter­nal work is now all done. The sil­i­cone will cure in 24 hours. 14 Mov­ing to the in­te­rior, the hatch in­te­rior fas­cia is trimmed down to suit ap­pli­ca­tion.

15 Hatch fas­cia is se­cured to the ceil­ing panel.

12 Ex­cess sil­i­cone is re­moved. 6

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