Cutting Roof Joists for Access

[Mudmonkey]

I’m just starting to turn my garage into a workshop and wanting to put my compressor up into the roof space as well as making it a bit easier to get in and out for other storage. 

Would it be safe/sensible to cut one of the roof joists and add trim pieces like the picture below akin to creating a loft hatch?

The joists are 4x2 and spaced at about 36cm. The roof is pan tiled. 

[zardos]

I'm not a structural engineer but logic says that by removing the centre joist you would be distributing it's load to the other 2, therefore it would be better to double up the sides in a fashion to retain the structural safety margin the original designer intended.
You might want to also double up the cross beams to stop them bending as wood is more flexible when pulled from the side.
Also make sure the joins of the cross beams to removed joist don't pull out under tension.

You might also want to put in a cross beam in the centre (I don't see one in the pics just some planks that are may be not fixed down) and may be some noggins again to stop flexing as you put new downward load on the joists.

Always better to be safe than sorry, you don't want the garage roof collapsing on you and your vehicle.

Edited December 29, 2018 by zardos

[Blanco]

Taking out a piece of 4x2 is common practice and the usual standard of replacement bracing is 'basic', what you propose would be fine in isolation for occasional access. Most roof structures however aren't designed to resist mechanical vibration. The aspect of your plan is the bit that bothers me slightly is putting the compressor up here. Nailed joints can shake out, joists and wall plates levelled on mortar might move and crucially the roof is going to effectively amplify the noise, Try it if you want but my feeling is you won't like the consequences. Much better to build a small kennel out the back or at the side, easier to drain etc.

[Arjan]

Storage up there is fine - but I would not like to have a compressor there...

If you need the floor space - hang is on the wall or on a rack but not in the attic.

 

[ballcock]

From what I can see of your roof structure the cross beams are there to stop the roof beams from pushing out with the weight, unlike a full truss which transmits weight to the cross beams. Cutting one beam as your plan will not be a problem, I would use some suitable length wood screws into pilot holes rather than nailing as the beam will be in tension. if you fix some flooring around the trap door it will also aid strength. As for putting the compressor above could you just put the reservoir up in the roof and keep the pump elsewhere?

[Mudmonkey]

Thanks for the pointers folks, my idea for putting the compressor up there was to actually mount it on some brackets screwed into the wall rather than sit directly onto the joists, isolated with rubber mounts and insulated to try to reduce the noise amplification.

I’ll give it a go and put it outside if it doesn’t work out. At least I know the roof isn’t likely to cave in if I make a bigger access hole 😆

[Paddy_SP]

I suggest that you fit an extension pipe to the drain with an easily-accessible tap so that you can empty the water out of the tank nice and easily - I do mine every time I use it as the air is horrendously wet at this time of year!