Fitting lintel to wall supporting false floor?

[electronicsuk]

I've just purchased a new house and I'm trying to get all the necessary work done on the property before I actually move in. The property is fitted with electric storage heating, and I'm hoping to replace this with a heat pump air conditioning system.

The hot/cold air will be run through ducting, and thankfully the downstairs portion of the house has wooden flooring supported atop large joists running at 90 degrees to a number of 2ft high supporting walls under the floor. The top of the final course of bricks before the joists have been faced with timber that appears to be around 1" in thickness and is attached to the wall by mortar.

These walls are there for the sole purpose of supporting the floor, and do not bear any other load. They seem to be constructed from typical house brick, and the blocks themselves have been 'staggered' so as to leave an approx. 2" horizontal gap between each brick where there would normally be mortar. That is to say, there is only mortar on the top and bottom faces of the brick.

Unfortunately, the ducting for the air conditioning is larger in diameter than the height of the joists, so running it between the floorboards and the top of the supporting walls is out of the question.

I have contacted a number of builders with regard to having a 700mm or so gap opened out under the floor in each wall to allow me to run ducting and also provide crawlspace for servicing. I've been let down a number of times and have not had a single one turn up to take a look at the job so far, and am looking to take the task on myself.

I have little/no building experience being an electrical engineer by trade, so any advice anyone can provide would be much appreciated. I'm interested in knowing if a reinforced concrete lintel will be up to the job, if trench props will be up to the job of supporting the floor while the work is carried out, and how much of the lintel should overlap the walls on either end. I'm also a little worried by the gaps in the wall and would like to know how this might affect their stability if I add a lintel.

I appreciate it's difficult to provide advice based on a text description, I can take some pictures tomorrow if necessary.

Kind regards

Matthew

 

[JerryM]

the concrete lintels are spot on for this application and use 150 mm overlap onto the brickwork at either end.

the trench props will also be fine (i use a car jack because the working ht is so small generally).

use a strong mortar 3:1 sand : cement to bed the lintel and try to use plasticer in the mix. leave the mortar for 24hrs before loading with the floor joists.

use typ wood packing under the joists (3, 6 & 10 mm) to level across the top of the lintel (if needed).

the gaps in the wall could be filled with mortar if you felt necessary. i don't feel it's essential though as the floor as a whole is pretty rigid laterally and the weight on the brickwork tends to keep the wall pretty well fixed.

 

[electronicsuk]

Thanks Jerry. In my haste I forgot to take any pictures when I visited the house earlier this evening, but from your advice it seems as if there wont be any major problems. I'll try and remember to let you know how it goes!