Should I set wooden porch pillars into, or on to concrete footings?

Question

I'm building a wooden porch on the front of my house. I have six 4" wooden pillars supporting the structure. It's light, doesn't contain concrete, roof tiles, etc, and is made entirely of wood. I'm digging footings and am about to install the pillars. I'm wondering whether to set the wooden pillars into the concrete or simply sit them on top.

I realise setting them into the concrete will mean they might move less laterally but I'm concerned that with the wood in the concrete there is more chance that moisture will slowly get in between the concrete and timber and rot the wood. It is not hardwood by the way. So should rotting occur in future, it will be easier to replace a pillar if they are not set in concrete - and I figure they are less likely to rot anyway if they are not set in the concrete in the first place.

So what's best - to set the pillars into concrete, or to just sit them on top?

My concrete footings are about 2.5 ft deep, 12 inches round for each pillar. I'm putting a metal mesh into each one to assist in concrete strength.

Answer 1

Set a steel pin (1-2cm diameter) or post-base-bracket in the concrete. Drill a hole in the bottom of the post for the pin, or attach the bracket to the post bottom - no lateral movement, also no accelerated rot. Rot is effectively guaranteed if you set the post into concrete. Brackets designed for the job maintain a small space between the concrete and the post. If you don't use that type of bracket, or you use a pin, set a small square of tarpaper/roofing felt/asphalt shingle on top of the concrete, under the post, to reduce water transport into the post from the concrete. A quick search indicated that post-base-brackets seem to be available in the UK, so that's the best option - tie the lower part of the bracket into your reinforcing mesh before pouring concrete. There are several typical options, this is one type (image from Simpson Strong-tie)

Answer 2

In my opinion, I would do what I could to keep the wood separated from the concrete, and any kind of puddling that would occur during the wet season. There is a type of post bottom that is galvanized that will handle any contact with dirt, pressure treated wood, what have you. Simpson is one of the brands, if your posts are 6"X6" the model is here. Others are linked on the same page. There are other manufacturers out there that make their own variation on the same thing. The idea is to get the wood up from the concrete, not just separated my the layer of metal. This one allows you to set a bolt after the concrete pour if you choose, and still allows for some adjustment afterwards for perfect centering.

Answer 3

Hmm I dont have enough reputation to comment individually being a noob, but just wanted to say thanks to both for those answers. The brackets are exactly what I was after, but I had no idea they existed. Thanks very much for taking the time to pass on the information. I'll get hold of those Simpson strong ties. Cheers all!