Sunday, June 19, 2011

Ask The Architect - Creating A Vaulted Ceiling

Answer

There are a couple of items to consider when converting a flat ceiling to a vaulted ceiling in a home of this era.  I live in a “contemporary” ranch styled home built in 1959 and I vaulted the ceiling in my bathroom when we remodeled it.
The first question to answer is structural.  How is the roof actually built?  If the house was built today it would more than likely be built with prefabricated roof trusses.  In that case there’s little that can be done, short of replacing the structural support for the roof and cutting out the bottom chord and intermediate supports of the truss.  This is probably the worst case scenario.
Transition in my home from vaulted ceiling to flat ceiling
Transition in my home from vaulted ceiling to flat ceiling
Fortunately for you, homes built prior to the mid 70s generally had “stick framed” roofs.  In this case it is possible to remove the ceiling joist and hang sheetrock on the rafters.  That is, it’s possible as long as the rafters are properly supported.  In the best case the ridge of the rafters are currently supported by vertical elements extending from a bearing wall below and the rafter span is short enough not to require intermediate support.  This is something that really requires an expert to look at for you to determine if the rafter support is sufficient and if it isn’t designing an alternative support.
The second question is insulation and ventilation.  Homes of that era were not particularly well insulated and there may be nothing up in the attic now.  A vaulted ceiling like this would generally be insulated in between the rafters and an air space of at least 1″ would exist between the top side of the insulation and the under side of the sheathing.  Here in Washington State the code requires R-30 insulation in vaulted ceilings.  The typical vaulted ceiling today is built out of 2×12s which leaves 2″ of air space for ventilation.
If your rafters are smaller than 2×12 (which they undoubtedly are) you can use dense insulation board rather than batt insulation which has a higher R value per inch of thickness.  Polyisocyanurate insulation has an R value that ranges from 5.3 to 8 per inch.  You could get R-30 out of 5″ of insulation.  If you have 2×8 rafters then you have no problem with insulation and ventilation.
Some parts of the country allow you to have no air space as long as the rafter space is FULLY filled with insulation.  Other areas of the country don’t have the same insulation requirements as we do here in Washington.  If you need to provide insulation and ventilation and your rafters don’t have enough room for all of that you could apply a layer of insulation to the rafters themselves and fasten the sheetrock through the insulation.  This would require extra long screws.
In order for the ventilation to work it needs to be “cross through” which means you need openings at the top and bottom of the rafters to allow the air to move through.  This is generally accomplished with vent blocking at the lower end and a ridge vent at the upper.
Finally you should consider attic access.  All parts of your attic need to be accessible.  If the vaulted area creates 2 attics then you’ll need an access to each of them.
That’s the long answer.  The short answer is that it is possible to create a vaulted ceiling in homes of that vintage but you’ll want a qualified professional to look at it and tell you what you need.  Good luck and let me know if I can answer any more questions for you.

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