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MR50 Monovent – Q&A

Q. Where would I use the MR50?

A. The MR50 is designed for use at top edge abutments of a lean-to pitched roofs to provide high level, continuous ventilation.

Q. How much ventilation does the MR50 provide?

A. The MR50 guarantees a continuous ventilation gap of 5,000mm²/m to comply with British Standard 5250 and Building Regulations.

Q. Can the MR50 be used if I have a window 100mm above the roof?

A. Our MR50 requires a minimum of 155mm above the roof. If the space above the roof is less than 155mm, we would suggest the use of our AV50 Abutment vent instead.

Q. Do I need to buy extra flashing with the MR50?

A. The MR50 is supplied with a lead alternative AluFlash apron flashing attached as standard, for dressing over the tiles. It can also be supplied with code 4 lead flashing on a made to order basis. Cover flashing should be used over the MR50 once installed.

Q. Is there a minimum pitch the MR50 can be used to?

A. The MR50 can be used down to a 15° roof pitch. If the roof has a pitch lower than 15°, it is classed as a flat roof as stated in BS 5250. A flat roof, in accordance with BS 5250, requires a higher ventilation provision, please contact the Glidevale Protect Technical team for further information at:

Q. What is included in the MR50 pack?

A. The unit comprises two PVC-U extruded sections (supplied in 1.22m lengths), complete with spacers, washers, screws and clips. The AluFlash apron flashing for dressing over the tiles is supplied as standard.

Q. Is the MR50 easy to fit?

A. The MR50 should be simple to install for those who have some DIY experience. It is supplied with fixing instructions and further advice is available from the Glidevale Protect Technical team on +44 (0)161 905 5700 if required.

A lead or AluFlash lead alternative cover flashing (not supplied) should be installed with the MR50 (as shown in the drawing below), in accordance with the recommendations of the Lead Sheet Association or as detailed within our AluFlash fixing instructions.

To provide the complete solution for new build construction, Glidevale Protect horizontal cavity trays with short lead or AluFlash cover flashing can be used.

Q. Where can I buy the MR50?

The MR50 with AluFlash flashing is available from the BPD Store at The product can also be ordered through most major building merchants and distributors. For large orders, please contact our Sales team on +44 (0)161 905 5700 or

To view our literature regarding the full Glidevale Protect Abutment vent range click here.

Related FAQs

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Stepped cavity trays

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Glidevale Protect is a division of Building Product Design Ltd.

Other subsidiaries include ventilation systems specialist Passivent and Kingfisher Louvres, manufacturer of aluminium louvres systems.

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