Elevated addition

[Tree-dweller]

DW and I are planning on a small addition to our house, with a twist: a bedroom elevated about 8- 10 ft supported on 6x6 posts with no foundation (due to the slope of our backyard). Anybody else have experience with such an addition? It was drawn up by an architect, but I still wonder what issues I should anticipate. Anecdotes welcome!

 

[RobbieB]

Might as well put a little covered porch under the overhang so you can have cocktails outside in the rain.

 

[Tree-dweller]

Believe me, DW already has thoughts along those lines!

 

[Philliefan33]

If you are in a place that has winter, be prepared for your bedroom to feel cold with all that unheated space below.

 

[travelover]

I added a 12x24 porch to the back of my garage that was supported by posts. The posts sat on poured concrete pilings below the frost level. I insulated the underside then covered the insulation with thin, painted plywood. After 27 years, it was still structurally fine. This was in Michigan - no earthquakes.

 

[H2ODude]

Be sure to have properly designed support of the 6x6 columns.

 

[pb4uski]

DW and I are planning on a small addition to our house, with a twist: a bedroom elevated about 8- 10 ft supported on 6x6 posts with no foundation (due to the slope of our backyard). Anybody else have experience with such an addition? It was drawn up by an architect, but I still wonder what issues I should anticipate. Anecdotes welcome!

I don't see any problem with it... our former summer "camp" and many similar structures are built on posts... in fact, I know a guy who is a contractor who lives in such a place year round.

You will want to insulate joists below the floor... I would suggest sprayed on insulation. You could then attach plastic panels to the underside of the joists and have an attractive outdoor area under the addition (assuming that you have adequate headroom).

Suntuf 26 in. x 6 ft. Solar Grey Polycarbonate Roof Panel-158912 - The Home Depot

I did something similar on my elevated outside deck.. I attached these to the underside of the deck and we have an attractive outdoor spot under cover... in my case it is insulated and I added some shimming to pitch rainwater that drips through the deck above away from the house... but it has worked out great for us.

 

[enginerd]

supported on 6x6 posts with no foundation

The posts cannot simply sit on the ground, I assume you will have some sort of post foundations or pier footings.

Couple of quick thoughts to ask your designer/architect:
Not sure how "professional" you are going with the addition. But if you are not going through a permitting process, I would be worried about getting a contractor and him treating your addition like a deck build-out with some walls and a roof.

Check the lateral stability. I've been on several covered porches that were "shaky". The posts were plenty strong, but not enough lateral support.

Also, you may want to design for wind uplift as a worst case scenario. Not sure where you live, but imagine hurricane or tornado force winds hitting the hill and being driven upwards on the bottom of your addition. Everything from your roof down should be strapped to the foundation. Although depending on your post foundation design, this may not be enough.

 

[meierlde]

The posts cannot simply sit on the ground, I assume you will have some sort of post foundations or pier footings.

Couple of quick thoughts to ask your designer/architect:
Not sure how "professional" you are going with the addition. But if you are not going through a permitting process, I would be worried about getting a contractor and him treating your addition like a deck build-out with some walls and a roof.

Check the lateral stability. I've been on several covered porches that were "shaky". The posts were plenty strong, but not enough lateral support.

Also, you may want to design for wind uplift as a worst case scenario. Not sure where you live, but imagine hurricane or tornado force winds hitting the hill and being driven upwards on the bottom of your addition. Everything from your roof down should be strapped to the foundation. Although depending on your post foundation design, this may not be enough.

Actually the posts will have to be placed below the freeze line to avoid having the building heave and sag in the spring (if it is an issue where you are building) That will be defined in the local building code.

 

[pb4uski]

OP's profile says that he lives in New England and the OP says that it was drawn up by an architect. While I agree with both of the above posts that the 6x6 posts will need to be on a suitable footing below the frost line, I would be amazed if that wasn't already covered by the architect, OP or later on the contractor since it is common practice in New England.

 

[meierlde]

OP's profile says that he lives in New England and the OP says that it was drawn up by an architect. While I agree with both of the above posts that the 6x6 posts will need to be on a suitable footing below the frost line, I would be amazed if that wasn't already covered by the architect, OP or later on the contractor since it is common practice in New England.

And also checked by the building inspector based upon the building permit, as a code requirement.

 

[enginerd]

I am also amazed all the time at stuff that licensed architects and licensed engineers can completely overlook.

 

[meierlde]

I am also amazed all the time at stuff that licensed architects and licensed engineers can completely overlook.

Look at some of the construction fail videos on YouTube and you see how even architects and engineers can screw up big time every so often. Examples include a column in the middle of a corridor, the shanghai building that fell over (10+ stories), the driveway with a 40+% slope, etc. Of course in at least some of the cases it could be the builder misreads or like in the KC Hyatt Regency balcony collapse figures out a "better way" to build and the better way means the balcony falls down

 

[travelover]

When I built my porch addition referenced above, the building inspector wanted me to install a conventional poured or block foundation. This was pre-internet, so I went to the library and got out the BOCA code book and showed him the section on building with pier construction. So, this kind of construction is not only acceptable, but covered by the codes to ensure that it is done correctly.

 

[pb4uski]

I am also amazed all the time at stuff that licensed architects and licensed engineers can completely overlook.

That reminds me of a funny story.

Back in the late 1970 I had a wealthy client who had built a gorgeous cow barn with a stained glass window in the gable end, a beautiful copper weathervane, etc. The milking parlor was oak posts and beams and inlaid tile.

A year after it was built I was doing the client's taxes and noticed that he spent a bundle on repairs. I told him that I was surprised that a one-year old barn would require so much in repairs... he told me that the first time they went to use the milking parlor that they discovered that the cows would not fit into the milking stalls... the big city architect had designed them too small so they had to tear them out and replace them.

 

[pb4uski]

When I built my porch addition referenced above, the building inspector wanted me to install a conventional poured or block foundation. This was pre-internet, so I went to the library and got out the BOCA code book and showed him the section on building with pier construction. So, this kind of construction is not only acceptable, but covered by the codes to ensure that it is done correctly.

What we did for my pool house and an elevated deck was to dig holes below the frost line with a post hole digger, put a flat stone at the bottom, then put a piece of suitably sized Sch 40 pipe in the hole and insert the post in the Sch 40 pipe... then plumb and backfill being sure to compress the back fill along the way. The frost grabs the Sch 40 sleeve and it and the surrounding ground move but the post stays put on the rock... we had that for 10 or more years before we sold the house and never had a problem.

While I'm certainly not suggesting this for the OP's bedroom, for small decks and outbuildings it works pretty good.

 

[Koolau]

Here in Paradise, many houses are built on hillsides and either large lanais or rooms are built out on posts. We looked at one house (during our house hunting) which had been built in this fashion. Apparently, there had been "issues" (though we were not told exactly what.) In any case, the old posts were abandoned in place and new, much more robust posts were installed to take the weight. My impression was that the new posts were perhaps 3 times as large as the old ones and were much more "professionally" installed (just a matter of my eye - not any expertise on my part.)

I wouldn't consider such construction without a thorough evaluation by an "expert" on the subject AND with the supports resting an very secure footings (or, as in many local homes) directly on the underlying bed-rock of the hillside.

It turned out that DW could not deal with the "concept" so we passed on all houses built with such techniques. It would not have bothered me, but she couldn't deal with it for some reason. She always seemed to think the "stilts" would eventually give way and that part of the house would become a toboggan. YMMV

 

[Tree-dweller]

Thanks all. Oh yeah, we are making sure contractor pulls all required permits. "Bigfoot" footings are to be below the frostline (min 4 ft), and the insulation in ceiling, floor and walls meets or exceeds the EnergyStar guidelines for my zone. That business Enginerd mentioned about uplift in strong winds, well that's one I'll have to ask about for sure! Might have to box in underneath.

 

[Hermit]

My first thought was how the knees would do on the stairs as you grow older, but I'm fast approaching geezer hood.

 

[NW-Bound]

A room addition that is on posts and sticks out from the house is basically a cube with 5 of its 6 sides exposed to weather. It will gain more heat than the rest of the house in the summer, and is colder in the winter. Good insulation and adequate duct work will be needed to make it comfortable. I know, because I have been there.

 

[Tree-dweller]

A room addition that is on posts and sticks out from the house is basically a cube with 5 of its 6 sides exposed to weather. It will gain more heat than the rest of the house in the summer, and is colder in the winter. Good insulation and adequate duct work will be needed to make it comfortable. I know, because I have been there.

Did you get the good insulation and adequate ductwork, and did it work, or did you wind up thinking it was a mistake to build it in the first place?

 

[target2019]

I'd think about over-engineering something like this. Being on a hill, I'd be worried about wind storms and the effects of water erosion on this structure. When an entire house sits on foundation, and a major portion sticks out, on stilts, that concerns me. What about home insurance? How much will it change?

 

[Koolau]

I'd think about over-engineering something like this. Being on a hill, I'd be worried about wind storms and the effects of water erosion on this structure. When an entire house sits on foundation, and a major portion sticks out, on stilts, that concerns me. What about home insurance? How much will it change?

As mentioned, we here have many, many such dwellings. Cold is not an issue, but heat and sun load certainly are. We don't do a lot of insulation - we usually just AC the heck out of everything OR have 3-side ventilation. Wind IS an issue. We do occasionally have hurricanes but more often have just plain high winds (40 to 50 mph isn't particularly uncommon.) I don't recall any issues of such dwellings "blowing over." We have lots of rain (at least on the windward side - and this year on the leeward side.) We do have some erosion problems from time to time, but again, don't recall too many houses going down because of it. We have much more problems with rocks breaking loose and crashing into someone's bedroom!

But target2019 made me think of something. If your insurance company is happy, you should probably be happy! Just a thought because YMMV.

 

[Bamaman]

I am also amazed all the time at stuff that licensed architects and licensed engineers can completely overlook.

I have a cousin and two close friends that are architects. I always said students should be required to work two years in the construction trades before they were allowed to start their architecture program.

 

[target2019]

As mentioned, we here have many, many such dwellings. Cold is not an issue, but heat and sun load certainly are. We don't do a lot of insulation - we usually just AC the heck out of everything OR have 3-side ventilation. Wind IS an issue. We do occasionally have hurricanes but more often have just plain high winds (40 to 50 mph isn't particularly uncommon.) I don't recall any issues of such dwellings "blowing over." We have lots of rain (at least on the windward side - and this year on the leeward side.) We do have some erosion problems from time to time, but again, don't recall too many houses going down because of it. We have much more problems with rocks breaking loose and crashing into someone's bedroom!

But target2019 made me think of something. If your insurance company is happy, you should probably be happy! Just a thought because YMMV.

Now that you mention 40-50 mph winds being common, sorta, I picture these homes around you as box kites with sturdy tails.


Do these architects take into account the direction that big winds may prevail from?

Probably makes a difference if you're surrounded by trees or perhaps other structures nearby.