Final pre start meeting - Groundworks/Foundation design

[epsilonGreedy]

20 hours ago, TerryE said:

Technically, yes but safer if you have 100mm.  Have a look at the blog posts a number of us such as Jeremy and myself on warm-slab construction which uses this approach.  The risk is that you really need a slab crew that are used to working with embedded UFH -- which isn't the case for most jobbing builders.  The devil is in the detail here and I've seen recent examples posted on the forum where members have shown how their builders made of total mess of doing this. 

 

The slab needs to be reinforced with mesh rebar.

 

 

Your advice seems specific to passiv slabs. The OP's design is not based on one of these.

 

In order to provide a more balanced view, what percentage of conventional B&B floors with UFH do you think are finished with rebar in the screed and the screed is +99mm thick?

Edited January 5, 2019 by epsilonGreedy

[ToughButterCup]

22 minutes ago, epsilonGreedy said:

[...]

In order to provide a more balanced view, what percentage of conventional B&B floors with UFH do you think have rebar and are 100mm thick?

 

Every single one of them...................?

[PeterW]

That floor barely meets regs - why not change it to Jabfloor units and put 225mm full fill beam units in and overlay with 30mm kingspan/celotex and use 100mm reinforced slab as the top finished floor. Would make it easy to work on and much more insulated. 

[epsilonGreedy]

15 minutes ago, recoveringacademic said:

Every single one of them...................?

 

Ok point taken, I have edited my question to be more specific.

[epsilonGreedy]

28 minutes ago, PeterW said:

That floor barely meets regs - why not change it to Jabfloor units and put 225mm full fill beam units in and overlay with 30mm kingspan/celotex and use 100mm reinforced slab as the top finished floor. Would make it easy to work on and much more insulated. 

 

Does winter weather influence this decision?

 

If the OP follows a conventional build route then the screeding can be delayed until the roof is on which probably implies fitting the UFH and screeding in the spring or summer.

[TerryE]

@epsilonGreedy, if you look at the elevation profiles then the beam and block would need to be dropped another 50mm to accommodate the screed. You can't have the internal FFL above the sole plate without courting disaster. The sole plate is anchored on a DPC at FFL.  The devil is always in the detail. ?

[epsilonGreedy]

3 hours ago, TerryE said:

@epsilonGreedy, if you look at the elevation profiles then the beam and block would need to be dropped another 50mm to accommodate the screed. You can't have the internal FFL above the sole plate without courting disaster. The sole plate is anchored on a DPC at FFL.

 

 

Maybe we are talking at cross purposes, not sure where the 50mm comes from. Anyhow I am not building TF and I think the OP has disengaged after the bruising feedback, it must be disheartening to be advised to start again after so much expense and preparation.

 

At the end if the day if the house shown in the OP was built as-is, are we debating more than £100 extra on the gas bill p/a compared to 150mm of under screed insulation?

[TerryE]

@epsilonGreedy, In another thread From wonky shelf to self build in deepest Cambridgeshire @Lots2learn talked more about his goals and explicitly stated:

 

On 26/08/2018 at 19:09, Lots2learn said:

I plan to be close to passive house but do not intend to go through the certification process.

 

So much of the advice is consistent with his wishes.  His stated U-values for walls etc. whilst not quite passive class are good enough to have a well insulated and energy efficient house -- that is with the exception of his slab design which is outside the general spec of his other house components.  This makes little sense to those of us who have completed our houses.  I don't think that anyone here has suggested a complete change to what was been done so far, for example switching from a foundation + beam and block floor to a passive floor.  I see this as an issue of making constructive suggestions going forward that can rebalance the design.  So if he wants to have UFH then replacing the blockwork with something like Tetris insulated blockwork is a option that is worth considering, IMO.

 

Also the detailed build-up of the floor profile is important.  The SE has to be willing to sign it off and his chosen builder has to be comfortable / competent doing it.  Are you going to have UFH or not? If so then how are you going to profile this up?  However it is done, the TF sole plate has be set above the internal FFL and DPC otherwise you risk wet rot of the sole plate and the compromise of the entire TF -- as I keep saying, the devil is in the detail.   Even if a classic radiator-based CH system is employed, a solid concrete floor significantly constrains the radiator placement as BRegs prevent you placing inaccessible joints in the slab, so need to design your CH topology and lay your runs unbroken before the pour.  Off the top of my head, I can't think of any members with new-builds of this class or better that have decided to go with a radiator solution for the GFL.  So the decision of UFH or not, upper floor heating approach, etc. really needs to be finalised at this stage before foundations and ground-floor finish are completed.

 

In another topic, I described the whole process of self-build a bit line skiing in front of an avalanche.  There is just so much to do and to lean and to get right and there is a logical sequence to be respected.  I am not saying I am good at this, but at least I was good enough to complete my house within spec and near enough to within budget, so all I am trying to do here is to help others avoid mistakes that can be avoided.

[ToughButterCup]

3 hours ago, TerryE said:

[...]

 I described the whole process of self-build a bit like skiing in front of an avalanche.  There is just so much to do and to learn and to get right.

[...]

 

Perfect.

To date I've fallen a couple of times, but thus far the snow's only up to my chin, still skiing as fast as Roadrunner  ...

[Declan52]

15 hours ago, epsilonGreedy said:

 

Maybe we are talking at cross purposes, not sure where the 50mm comes from. Anyhow I am not building TF and I think the OP has disengaged after the bruising feedback, it must be disheartening to be advised to start again after so much expense and preparation.

 

At the end if the day if the house shown in the OP was built as-is, are we debating more than £100 extra on the gas bill p/a compared to 150mm of under screed insulation?

At the end of the day it is going to be  his choice to take on board all the advice given here.  If he wants ufh in his ground floor and wants it to heat the house then the floor needs more insulation.  It's just that simple.  If it's left as is then the heat loss to the floor underneath will be too much that the ground floor will struggle to  get to a nice liveable temp without either it being on permanently or the water temp being  over 50 degrees or maybe even both. These two options will be much more expensive in the long run than extra insulation or a different flooring system. 

But it's his choice. 

I don't think that he has actually started so there is still time to make alterations using a pencil rather than a digger.  

[Lots2learn]

Hi All,

First of all please don't interpret the breaks between my responses as me cowering in the corner from the posts on this thread.  I have a very thick skin.  I understand the passion this process engenders in those who set out to build their own home.  Unfortunately work commitments keep me away from the keyboard for several days at a time.

The feedback I have received is mainly centered on the ground floor build up and it is in that area I am now focusing my attention.  It is a little late in the day to radically change the design.  I know some of you will be screaming at your screen that if not now when.  However, there are other factors at stake and further delays, we were due to break ground last October, are going to have a significant impact on related projects and plans.  I am now looking at Tetris B & B system and awaiting details of how this product could be incorporated in the design without significant amendment.  I am also looking at Jabfloor products.

To address the remarks I made when I first introduced myself last year about wanting a near passivhaus performing property this was true.  However, the design of the house, the orientation in the plot and the shading by trees in neighbouring properties has meant that this goal is out of reach and so my expectation has altered.  This came to light after PP when I started to assess the heating requirements of the property based on some fairly crude assumptions which are now proving to be not too inaccurate. We will have a beautiful home that will be highly adaptable and will be able to change to meet our needs as we grow old with it.  It will be warm, well insulated, low maintenance and distill all of the best features of the many houses we have lived in up to this point.  Our design team were chosen for many reasons but at the very start they were open that they had never worked with T/F before but having short listed several architects this team were the ones we felt most able to work with.  They had a lot of experience in working with the planning authority in the same conservation area in which we are building and have achieved PP where many had questioned whether it was worth the effort.  We are learning together the joys of this process and they have done much more than they have been paid for and in the last few years have become friends whom I trust.  My PM, there is a team of 2, are very experienced self build and T/F builders and come highly recommended by several self builders who have used them in our area.  I have visited many of these properties and I am very impressed by the quality and attention to detail they have incorporated. They will be sub contracting out the various elements of the build so we will not have a main contractor.

So please do keep your suggestions flowing.  Remember we all start this process at different levels of skill, knowledge, experience, priority, time and budget but we all hope to get to the same point! I am minded to start a blog on here but wonder if these threads are more likely to be open to a wider audience for comment.

[Declan52]

Every one starts their build with high hopes and the wish list.  As things progress then you start to realise what effect various different aspects of orientation and site layout can have,never mind budget . If you have to make changes then make them, as it's you going to live in the house.  

You seem to have all your Ducks lined up so do your research on each stage and if you need a question answered post away.

As for a blog its just an easier method to record your progress as you can divide it up to suit the different stages that you encounter.  On a single long post the details very quickly get  lost as posts can detour of  topic. Have a read through a few and see if it's something that would interest you. 

 

[Ferdinand]

36 minutes ago, Lots2learn said:

So please do keep your suggestions flowing.  Remember we all start this process at different levels of skill, knowledge, experience, priority, time and budget but we all hope to get to the same point! I am minded to start a blog on here but wonder if these threads are more likely to be open to a wider audience for comment.

 

Great attitude.

 

It is far better to have more feedback and reject some than to not be told things and find out later that you really needed that extra insulation underneath your now-built house.

 

F

Edited January 6, 2019 by Ferdinand