GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Midbass Horns and Real Estate.

Post Subject: It's not so bad really.Posted by miab on: 1/30/2010

Nice drawings Romy. It's looks from them that it is not too bad a situation IF your dealing with roof rafters and not trusses. Trusses look similiar to this link:

http://www.google.ca/imgres?imgurl=http://www.cedar-log-homes.com/Small-stuff-images/TypicalRoofTruss.gif&imgrefurl=http://www.cedar-log-homes.com/Roof-trusses.htm&h=324&w=524&sz=5&tbnid=ltCHYCKQAXwzXM:&tbnh=82&tbnw=132&prev=/images%3Fq%3Droof%2Btrusses&hl=en&usg=__wz1x2t73z1ooUnCooiDP6r-ga5M=&ei=_25kS-HZGsrh8QbBqOWdAw&sa=X&oi=image_result&resnum=8&ct=image&ved=0CCcQ9QEwBw

Roof rafters in a traditional type look like this:

http://www.timber.org.au/ewebeditpro4/upload/Nom_roof(1).jpg

First, your cathedral roof is using the structure of the attic roof for support where it starts to blend with it and maybe the internal wall of the attic capped room. Is there a little bulkhead where the two rooms join? That would be a little protrusion of the ceiling at that point. If so, there will be a support beam there. Keeping a center post between the horns like you have in the drawing will help. The triangular part (if looking from above the house) moving up the attic roof to the end point of the triangle is using each roof rafter for support. Especially with snow load in Boston you don't want to just cut any out. Your right about having a professional look before you cut. If you're to do it 'official' you will also need city approval when dealing with structure. That being said, it is not at all a huge undertaking. The horn building will be the more dificult part of the project.

You would reframe the roof of the attic space as you would, for example, a huge triangular window dormer. You see these little peaked windows popping out of the roof as you drive by older neighborhoods.

Want I want to stress and is more important than I think you took it in an earlier post is the condensing factor within the horn and back cavity. The temperature difference between the attic (cold in winter/hot in summer) and room below (warm in winter/cool in summer) will need to be dealt with. The best and most thorough solution to this is to insulate/vapor barrier/sheath the underside of the roof rafters and condition the space. Actually make the attic or the part where the horns are, part of your living space. Either take a duct run and return air up there from existing furnace utility (you can keep the ceiling under the horns this way. Or open the attic space as an extension of the cathedral ceiling of the perpendicular room and have the normal warm air rising heat the space and put a ceiling fan in to help in summer getting the warm air out of the peaks.

If you want to just insulate around the horns and back cavity, take care putting in a complete vapour barrier on their exterior and then wrapping them with (I think in Boston) R30 or R40 blanket. This is not ideal but doable but you might run into issues later.

All the above is if your NOT dealing with roof trusses. Trusses are a different animal and need to be totally restructured if you want to do what your thinking. That involves taking the whole roof off. Not fun and I would never do it.

BTW I very much like plan A and NOT plan B. That view of the forest is spectacular and will just add to the benefits and enjoyment of your first home purchase, audio aside.

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