Changing design to vaulted ceilings - help with service void / insulation

[boxrick]

I am having a complete new roof on my existing house and extension. The design is to have roof lights punching through holes and a raised ceiling. 

However now I am just contemplating just vaulting my ceiling instead and to stop messing about with something I only half want, my roof is already very shallow and my floor is very high so I want to maximise ceiling space

 

• So based on that, what would be a sensible makeup of insulation to get equivalent performance to below?
• Would I still be able to have a service void for electrics, MVHR on warm side? 
• Any recommendations before I go ahead and try and get this changed?

[ProDave]

Vaulted ceiling requires you have a ridge beam running end to end of the roof, and then probably larger rafters hung from that down to the eaves.  It completely removes the need for the raised tie and all the truss members, leaving you a simple roof easy to detail.

 

In our case we built as a hybrid roof, 195mm deep rafters, full filled with insulation and 100mm solid insulation above the rafters.

[JohnMo]

All our rooms are vaulted. As @ProDave says you need a ridge beam then either plain timber, pozi rafter etc.

 

Our pitched roof is 256mm pozi rafter, then below we have 2x 50mm battens, then 356mm of insulation full fill. Below we have airtight vapour barrier, a further 50mm battens and then plasterboard. Above we have 22mm sarking boards, vapour open membrane, and then slates direct to sarking boards.

[boxrick]

So actually aside from this ridge beam, everything else actually becomes simpler really. 

And how about this service void?

[boxrick]

This was the comment from my architect:

 

Quote

It will need a whole new structural design for the roof. Potential problems are if you ended up needing purlins for the larger span roof over the bedroom and kitchen making it more complicated than a couple of big ridge beams and bigger rafters. Also if you want it fully vaulted with no break in the ceiling line between kitchen and living then it’s more complicated structurally but ideally would need to be done because it will look funny to have a big triangular bit of wall at high level there.

 

There are a few options so  first you will need to explore the possibilities with structural engineer. Ask them to give you feasibility design options for a fully vaulted ceiling in the bungalow and see what they come up with.  See if David will do some concept sketches as to your options to structurally to make it work.  Then see if it’s still feasible when you see what he proposes.

 

I think it’s a bit late in the day to change it now, you are almost ready to order the raised-tie trusses and it will cause a delay to get structural designs and architectural changes, whether it’s someone else or me.  I cant do any big changes for 4 weeks. If you get someone else see if they can do a 3d drawing so you can appreciate the issue where the two different roofs join.

 

Plus you would have all your pipework on display as there would be no roof void.

 

 

[JohnMo]

39 minutes ago, boxrick said:

Plus you would have all your pipework on display as there would be no roof void.

Not strictly correct. With a service void, pipes can go in there, or with the actual roof structure. We have all hot water pipes and MVHR ducts within the roof structure and within the insulation. Green are the MVHR ducts, white hot water pipes. 

 

[ProDave]

2 hours ago, boxrick said:

This was the comment from my architect:

 

 

That reads as someone that got the hump because you want to change something.

 

Yes it will need some SE design.

 

As for the rest pipes will be on display?  How many pipes do you expect to have going into a vaulted ceiling and just where will they be going?  Exactly  NONE. They all go through the service void in the walls.

 

MVHR vents are the only ones that can be tricky. But each case is individual and you will find a route.

 

And just because the structure is built as a vaulted roof which makes building a good air tight well insulated building a lot easier to detail, you do not have to have all rooms open to the roof space.  We had one bedroom fully vaulted with a mezanine floor as a feature.  The master bedroom was partly vaulted with a higher ceiling but still giving a loft space above it, and the landing and bathrooms had normal 2400mm ceiling giving a larger loft space above them.

 

So much flexibility and options you can choose as you go.  And any loft space you do choose to create, will be just as warm and dry as any other part of the house.

[boxrick]

My ceilings are really shallow anyway so any loft space is none existent. But as you say it just gives me ultimate flexibility.

I have contacted my structural engineer asking for help, I appreciate the advice everyone

[SBMS]

54 minutes ago, boxrick said:

My ceilings are really shallow anyway so any loft space is none existent. But as you say it just gives me ultimate flexibility.

I have contacted my structural engineer asking for help, I appreciate the advice everyone

Do it! We are using 304mm engineered posi rafters filled with cellulose, right to wall plate, hanging off a steel ridge beam. Really simple and maximum floor space with no purlins required. I would have no idea why you’d be putting pipes in your roof to be honest. Mvhr doesn’t have to be ceiling bound (especially if a bungalow?). Counter battening 50mm below allows you to run electrics and spots fairly easily. 
 

Mitek or similar will do you a design for free -

obvs you’d need SE to ensure walls are supporting, specify beam sizes etc. 

[ETC]

Very simple to do. Ridge beam plus rafters. Ceiling ties below can create a service void as large or as small as you need. Your ‘architect’ is talking balls.

[boxrick]

Shes pretty good to be fair, but I think I have made so many design changes at this point I am driving her mad.

Regardless I have just contacted Mitek asking for help with a design. Thanks for the push in the right direction. 

Does anyone have some diagrams or similar to help me understand what it may look like in respect of my 'service void'?  I would like to approach passivehaus levels of insulation or as close as I can sensibly get. 

[SBMS]

22 minutes ago, boxrick said:

Shes pretty good to be fair, but I think I have made so many design changes at this point I am driving her mad.

Regardless I have just contacted Mitek asking for help with a design. Thanks for the push in the right direction. 

Does anyone have some diagrams or similar to help me understand what it may look like in respect of my 'service void'?  I would like to approach passivehaus levels of insulation or as close as I can sensibly get. 

Here is our design. We probably won’t even put the collar detail in and keep it vaulted as high as possible

 

Edited Tuesday at 21:04 by SBMS

[boxrick]

13 minutes ago, SBMS said:

Here is our design. We probably won’t even put the collar detail in and keep it vaulted as high as possible

 

Thanks so much for sharing this, can these red lines I have added in work as a service void for MVHR pipes and roof lights? 

[SBMS]

4 minutes ago, boxrick said:

Thanks so much for sharing this, can these red lines I have added in work as a service void for MVHR pipes and roof lights? 

Yep. That’s exactly what we are doing - architect didn’t draw it but we will be counter battening the entire inner surface of the smartply, running services/spots in that and then plasterboarding on top. You can get 50mm flat MVHR ducting but you could also do wall outlets (or even floor outlets). 

[boxrick]

12 minutes ago, SBMS said:

Yep. That’s exactly what we are doing - architect didn’t draw it but we will be counter battening the entire inner surface of the smartply, running services/spots in that and then plasterboarding on top. You can get 50mm flat MVHR ducting but you could also do wall outlets (or even floor outlets). 

Ahh ok 

And any reason warmcell insulation instead of something like Knauf Earthwool Rafter Roll 32? 

[SBMS]

20 minutes ago, boxrick said:

Ahh ok 

And any reason warmcell insulation instead of something like Knauf Earthwool Rafter Roll 32? 

It gets blown into every nook and cranny so reduces the dependence on skilled labour to fit. It also gets blown in between the metal web which would be tricky to do with rafter roll. When I priced up both they were very similar priced. 

[Nickfromwales]

Glulam ridge beams, posi-joists, full-fill with blown warmcell, and put the MVHR ducts in the joist voids on the warm side (mechanically fixed to the inside of the lower chord), and jobs a good 'un.

 

Service battens in front of your AT membrane, and then you cables can run through there.

 

I was going to say your architect seems to have run out of steam, but kudos to her if you're the one who's worn her down. We're all only human at the end of the day.

 

I asked about this roof in your MVHR thread, I have my answer now lol.

 

Where i designed and installed all the M&E for a client with an MBC TF PH build, I worked with MBC and the client (and their architect) to provoke some structural changes; to keep the bedrooms and open spaces vaulted etc, and then created a small attic over the ensuite to house the MVHR in a warm section that we dedicated to that cause. Got the MVHR out of the 'living space' without any real impact to the overall 'look'.

 

I've done this more than a few times now, where the architect (and often the client also) do not appreciate how much room M&E equipment needs, and how bulk items can be lost into the fabric of the build with a bit of ingenuity and GIF.

 

My USP is solving problems that others see as "too much like hard work", it's not really that hard tbh.

[boxrick]

 

My builder seems to think we can rest on this current external wall ( it will be internal soon ) which will make the span shorter and all this simpler 

My structural engineer has said 'It will be steel ridge beams with timber valley beams and rafters' I have asked him to do the structural calculations for this

I also contacted Mitek who said they can help, but said only through one of their manufacturers, so I reached out to 3 near to me and am awaiting replies.

I think the final thing here is my roof insulation construction is going to be completely different now, currently thinking 300-350mm of Knauf Earthwool Rafter Roll 32 or warmcell as mentioned above