Beam Choices

I have had complaints, and no wonder. Jill & Bill for one are after an update, and I can only apologise for my tardiness. The date of this post is June 16th, but this is a total lie as it is July 7th today. However, this is the first of a series of posts that should bring you up-to-date. There is no excuse, other than time spent watching the world cup, tending my allotment and following Le Tour De France.

So, beam choices. You may remember that we engaged an alternative Structural Engineer to carry out some calculations for the longer steelwork needed to bridge the gap where the straight staircase was going to be. Well, after a few conversations we received some preliminary drawings today, and we have a choice. There is also a complication.

First the complication. The plans for the extension quote a pair of steel beams bolted together, and with a depth of 203mm. The idea, as we understood it, was that this allows us to have a flat ceiling in the room below - no step down intrusion of the beam. However, the new Structural Engineer says that this is flawed. Firstly, a 203 beam is actually 216mm deep. Secondly, you are supposed to fly the flooring above the beam to the tune of 12mm (minimum) clearance to allow for joist shrinkage. Thirdly, the specified 200mm joists actually come out nearer 195mm after finishing. So, unless we use battening, or other spacers of some sort, even the current design will give us a step down ceiling (officially referred to in the trade as a "downstand").

Now for the choices. Firstly, the option of having two beams bolted together is no longer possible over this sort of distance. I don't know why, even after two telephone discussions with the Structural Engineer, but he assures me it is not possible. So, using a single beam, there are two main ways to make it stronger :

1. Make the section deeper
2. Use thicker metal throughout.

The first option is a 203x203 @ 71kg/m. This has the same depth as the original beams, so the downstand will be unchanged at 33mm. Trouble is that this is very heavy at nearly half a Tonne and will take some manpower or machinery to manoeuvre into position. The second option is 305x127 @ 37kg/m. This will give a calculated 122mm downstand. Other than the difference in downstand, the big differentiator between the two is the cost. The beefier beam has over double the amount of steel than the deeper, but thinner section, so will obviously be more expensive.

The builder wants to place an order on Monday, so we have to choose over the weekend. His preference is the deeper, lighter beam, but then it would be as it is him and his team who have to move it around the site ! Our perspective is a little different. We are concerned that the large downstand will bring the ceiling too close to the top of the windows. We could, of course, box in the beam and have it visible across the centre of the room. There are some very fine houses around the country with just this arrangement. However, they tend to be a little grander than ours, and we are not sure it will work here.