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Rafter Styles for Porch?

Posted by keithdirt (My Page) on
Sun, Oct 28, 12 at 18:38

I have a curious question about carpentry on roof rafters.

Our large front porch was finished while we were gone a week, big mistake as the style did not turn out like we specified or much like the drawings our architect gave us. I usually hang around during big parts because already I've saved some big problems from happening. Ironically, I'm not a carpenter by any stretch of the imagination, but I do possess some logic.

The underside of the porch features a box that is 6 inches deep from the inside ceiling across the length of the porch, above the pillers, and across the two ends. (see pictures). We were supposed to have a flat underside, with the pillars at 8 foot. Instead we got this box effect and the pillars (which we purchased) were cut down to 7 foot 6, a full 6 inches less than spec'd.

After looking at a few other porches, about half had this box thing and half were flat, so it's not horribly WRONG per se, just not what we were wanting.

I have a feeling that this happened because of the rafter style they used, where the rafters sit on top of the chord instead of sitting down inside of it, allowing the entire structure to not only sit higher, but getting rid of the box that is enclosing the beam the rafters sit on, thereby giving you a flat ceiling on the porch instead of a boxed effect.

Are there two different styles of rafters and the carpenters chose one over the other, perhaps the easiest route?


Follow-Up Postings:

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RE: Rafter Styles for Porch?

Your rafters overhang the supporting beam so they have to sit above the beam. The only way that the rafters could have been flush framed to the beam is if the supporting beam was at the fascia line and there was no rafter overhang. Hope this helps!


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RE: Rafter Styles for Porch?

On closer examination, it appears that your porch is a lesser dimension than your roof. Is this the case? If so, that's what determined where the supporting posts (columns) had to be placed.


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RE: Rafter Styles for Porch?

A "pillar" is a general term for an upright building support element; a "colummn" is a pillar with an identifiable base, shaft and capital like yours.

Your columns are obviously intended to be replicas of classical Doric columns all of which would originally have supported a 3 part horizontal "entablature" that would support a sloping roof overhang called a "cornice".

For a simple porch structure normally only the lowest horizontal band of an entablature, the "architrave", would be used. It would be plain and slightly narrower than the width of the "abacus" (the square top piece of the capital) and look like a "boxed beam" running across the tops of the columns. In fact, today it usually does contain the wood beam that supports the rafters.

This appears to be what the carpenters built so I would give them higher marks than your architect who I hope just forgot to show the architrave on the elevation drawings. But I would have made it a bit deeper since it rests on such formal classical columns.


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RE: Rafter Styles for Porch?

While the columns are classical, there's little else that's classical here, as far as I can see. And from looking at the porch, it doesn't appear that the columns could have been placed any further forward beneath the roof.

My guess is that the porch was built first, and it determined the location for the columns. I'd guess that thereafter the roof pitch and overhang were simply calculated to match the rest of the house and the framing completed.

Did the drawings should some other type of construction?
T


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RE: Rafter Styles for Porch?

I think the OP expected the ceiling of the porch to rest directly on the column capitals.


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RE: Rafter Styles for Porch?

I have to say that porches detailed outside the classical conventions are one of my pet peeves. Thought I'd show some of my carpentry work :)
Here's a tiny but authentic classically-inspired portico I designed and built many years back. The homeowner supplied the salvaged collonettes.
Smith portico, Built in benches.

This porch was designed (not me) in a late-Victorian style, but adheres to the classical idea of the lintel/beam being visible:
Porch  and new deck completed

This portico, on a more massive scale, has a complete entablature, but with an arched frieze that lends a Victorian feel:
Finished Portico

Finally, a very modern house with a minimal beam line, but still there; I think it was about 6" high.
Renfro House, Sheperdstown

I really do not care for porches that have columns supporting a flat ceiling with no beam visible. They just lack a visual sense of ease or gracefulness, IMO.
Casey


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RE: Rafter Styles for Porch?

Casey, thanks for these photos: they are gorgeous (except perhaps for the last example, IMO). Now if something like one of these was what the architect designed for the porch of keithdirt, I'd be having the GC remove and reframe the porch. It's all a question of what was designed and what was built.


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RE: Rafter Styles for Porch?

They could have recessed the header so that the ceiling was completely flat with no box. As you said some houses have it one way and others have it another so it comes down to your preference.

Personally, I like the beam/upper enclosed area of our front porch. We drove around our neighborhood to see what our preference was and realized we wanted the header dropped as the completely flat ceilings were too open, in our opinion.

Figure out what you prefer and if its a completely flat, no box ceiling speak up now to your GC


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RE: Rafter Styles for Porch?

It would be an architectural joke to use replicas of ancient Greek/Roman fluted Doric columns but omit the element that connects the tops of the capitals and carries the load of the roof.

It doesn't need to be a full entablature but it should at least be a modified architrave/boxed beam.

Roman Doric temple detailing
Image and video hosting by TinyPic

Modern porch adaptation
Image and video hosting by TinyPic


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RE: Rafter Styles for Porch?

The carpentry framing to create a: 1) classically correct architrave and pitched roof framing, or 2) a common residential porch roof couldn't be more different.

It all comes back to what was the design and what was built? And where was the normal supervision?

This isn't a case of "coulda, woulda, shoulda"!

Construction should follow the design drawings. Lacking design drawings, one cannot fault builders for wanting to use their common experience. In that case, where was the supervision before, during and after construction?

This is what a design and construction partnership is all about, and how undesirable results are dealt with (if that's what they are)!


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