MVHR and rooflights

[Adsibob]

I have an openable Velux, measuring 134cm wide by 160cm long going in my loft conversion. Originally it was going to go in quite near the top of roof, starting about a metre away from the ridge (measured along the diagonal of the roof slope). This size in the spec I wanted only comes as a centre pívot. Architect has now recommended we move it down by about a metre along the diagonal to improve light coming in to the floor below. The problem with this is that instead of having 2.1m under the open velux, we will only have 1.5m. This basically means it won’t really be possible to open it more than just ajar, as otherwise it would create a head hazard as one is going up and down the stairs.

 My question is, how much of an issue is this given we will have MVhR? Most of the year, we won’t open the rooflight, but I thought that in hot summers it would be helpful to open it to help cool the house. 

[ProDave]

You don't want to open a centre pivot wide anyway or else it will get wet inside when it rains.

 

I would be more concerned with BC getting upset if headroom above a stair was less than 2M with the window open.

 

 

[Adsibob]

Panic over. Architect has drawn it up in CAD and shown me that with window open there is still 2.1m of space. I had forgotten that the rooflight sits where the tiles are, and calculated the distances from the ceiling, ignoring that the skylight is recessed within it.